Carl Friedrich Christian Mohs's Mineralogical Legacy

Carl Friedrich Christian Mohs, lithography by Joseph Kriehuber (1832).

Talc – Gypsum – Calcite – Fluorite – Apatite – Feldspar – Quartz – Topaz – Corundum – Diamond - the Mohs Scale of Mineral Hardness is familiar to rock-hounds and earth-science students alike. The ten-point hardness scales lists common minerals in the order of the relative hardness, with talc being the softest and diamond the hardest mineral found in nature.

The Mohs scale is named after German mineralogist Carl Friedrich Christian Mohs, born January 29, 1773, in the town of Genrode, at the time part of the principality of Anhalt-Bernburgs. After attending school, he worked in his father's business as a merchant, but in 1796 he went to the University of Halle to study there mathematics, physics and chemistry. He continued his studies at the famous Royal Saxon Mining Academy of Freiberg, where he studied under the renowned geognost Abraham Gottlob Werner. Werner published in 1787 a »Kurze Klassifikation und Beschreibung der verschiedenen Gesteinsarten« - Short classification and description of the various rock types - as a guide for identifying and classifying rocks and minerals. Unlike other mineralogists at the time, mostly using chemical analysis, Werner uses easily recognizable features, like color or crystal shape, to classify minerals and rocks. Mohs is impressed by Werner's approach. In 1804, he publishes himself a “student-friendly” classification chart for minerals, based on his experience in the mining district of the Harz mountain and as a consultant for wealthy mineral-collectors. In his book »Über die oryktognostische Classification nebst Versuchen eines auf blossen äußeren Kennzeichen gegründeten Mineraliensystems« - The genetic-geological classification and an attempt to introduce a mineral-system based on outer properties - Mohs combines various physical properties of minerals, like color, hardness and density, with six classes of crystal shapes, to identify 183 different minerals.

Mohs scale of hardness sets from the 19th century, Mohs's geological hammer, and a letter to his wife.

Mohs continues to travel, collect material and improve his mineral classification system. He visits Štiavnica in Slovakia, famous for the local Mining Academy, and the mining district of Bleiberg in Carinthia. He visits and studies mines in Hungary, Transylvania and Scotland, and quarries in Germany and Austria.

In 1812, now a professor in the Austrian city of Graz, he creates a preliminary hardness scale and continues to publish guidelines for mineral identification. In 1818 he returns to Freiberg and between 1822-1824 Mohs publishes his final version of the hardness scale in the book »Grund-Riß der Mineralogie« - Essentials of Mineralogy.

The Mohs scale of mineral hardness is based on the ability of one natural sample to scratch another sample visibly. The samples of matter used by Mohs are readily available to a student or miner. Minerals with a hardness of 1 or 2 can be scratched with a fingernail. A coin will scratch minerals with a hardness of 3, the blade of a pocket knife scratches minerals of the hardness 5 and 6. Glass will scratch minerals with a hardness of 7, and harder minerals scratch each other.

Calcite crystals, example of a common mineral with hardness 3.

The British Diplomat Who Studied Volcanoes

When, in 1631, Vesuvius erupted violently after having been dormant for more than 300 years, it aroused great interest among Europe's elite. German Jesuit and naturalist Athanasius Kircher traveled to Southern Italy to study Vesuvius, descending even in the crater. The volcano was almost continuously active, especially after 1750 and Naples became part of the cities traveler should visit when in Italy.

Sir William Hamilton (1730-1803) was a British diplomat in Naples from 1764 to 1798, He got so interested in the nearby Mount Vesuvius that in 1776 he published a monograph on the mountain, illustrated with stunning artwork by local painter Peter Fabris. Hamilton's "Campi Phlegraei: Observations on the Volcanos of the Two Sicilies" is considered a pioneering work of early volcanology.

 The eruption of Mt. Vesuvius in August 1779.

The eruption of May 1771. An Aa lava flow (recognized by the broken surface texture) passes the observer's location and reaches the sea at Resina. Note the steep, slowly advancing front of the flow. Pietro Fabris is amongst the spectators (below left) as is William Hamilton, who explains the view to other onlookers.

Inside the crater of Mount Vesuvius.

Lava samples from Mount Vesuvius.

Another view of the August 1779 eruption of Mount Vesuvius.

The excavation of the Temple of Isis in Pompeii.

 Hamilton at the crater of Forum Vulcani (Solfatara near Pozzuoli), examining the sulphur and arsenic deposits near the hot springs.

Historic Mineral Collection Destroyed in Brazil's National Museum Fire

German mineralogist Abraham Gottlob Werner was born in 1749 in Wehrau, at the time a city in the Prussian kingdom.
Werner was educated at Freiberg and Leipzig, where he studied law and mining. In 1775 he was appointed as inspector and teacher of mining and mineralogy at the small, but influential, Freiberg Mining Academy in Saxony. Here he catalogized the collection by mining inspector Carl Eugenius Pabst von Ohain (1718-1784) consisting of 7,500 mineral and rock samples. The collection was also used to teach mineralogy and petrology at the academy. After the death of Ohain in 1785 the collection was sold to the Portuguese statesman, author and amateur botanist António de Araújo e Azevedo, 1. conde da Barca. In 1807 the mineralogical samples were shipped to Rio de Janeiro, where they were incorporated in the collections of the newly founded National Museum of Brazil. Werner started a new collection, still hosted today at the University of Freiberg. In 1787, based on the studied collections, he published “Kurze Klassifikation und Beschreibung der verschiedenen Gesteinsarten” (Short classification and description of the various rock types), a classification guide using - unusual at a time when most rocks were classified based on the complex rock-chemistry - easily recognizable features (like color, shape, even odor) to identify minerals and rocks. Werner's works play a very important role in the history of geology and mineralogy. He named many common and less common minerals, like Kyanite and Vesuvianite in his writings. His books on minerals and rocks-identification influenced an entire generation of German geologists, including Alexander von Humboldt. Charles Darwin used "Werner’s Nomenclature of Colours" published in 1814 and based in part on A.G. Werner's work, to describe his rock and mineral samples collected during the famous voyage of the Beagle.

Unfortunately, a fire destroyed the National Museum just a few days ago. The extent of the fire's damage won't be fully known until salvage efforts are completed, but it is feared that also Ohain's mineral collection is lost.

After an enormous fire destroyed the National Museum of Brazil in Rio de Janeiro on Sept. 2, 2018, the Bendegó meteorite was one of the few artifacts left relatively intact. The meteorite is the largest space rock ever discovered in Brazil. 

Will democracy survive climate change? - A lesson from the past

Allegory of volcanism as bringer of fortune (fertile soils) and destruction, by artist Alexandre-Évariste Fragonard (1780-1850) after a draft by French naturalist Joseph Nicolas Nicollet (1786-1843).

In June 1783 a volcano in Iceland erupted. Volcanoes are nothing unusual in Iceland, but this eruption, later referred as Laki,  was different. For eight months volcanic ash and gases poisoned the atmosphere over Europe changing the climate for years to come. In Europe the exceptionally hot summer of 1783 was followed by long and harsh winters until 1788. Crop harvests were poor and bread, essential for the large and poor population on the continent, experienced a massive price increase.

Map showing the lava flows of Lakagigar, from Magnus Stephensen "Kort Beskrivelse: Vester-Skaptefields-Syssel paa Island" (1785). The lava from the fissures ended up covering an estimated 2,500 km² (965 sq mi) of land.
 

At the time France was characterized by a great inequality between the poor peasants and the upper class. The rich aristocracy and the corrupted clergy lived in an own world, distant from daily problems. The lower and middle class had no political power despite its important role in economy and the king was to weak to control the aristocracy. Poor harvests and war expenditures resulted in an economic crisis and famine spread. In human history hunger was always a powerful agent of change. Italian officials noted in 1648 during a widespread famine that “it was always better to die by the sword than to die of hunger.” Women revolted on the streets demanding bread. July 14, 1789 5,000 citizens of Paris stormed the Bastille. Years of chaos followed. French lawyer Maximilien Robespierre instituted an authoritarian regime, culminating in 1793 with the execution of king Ludwig XVI. followed by 16.000 other people only in Paris. In 1799 Napoleon Bonaparte promised to bring order in those chaotic times and in the end declared himself emperor - celebrated by the same people that just some years earlier battled an absolute monarch. Even if the French Revolution is often seen as starting point for the modern Europe, democracy was predated by tyranny.

Georg Heinrich Sieveking’s “Execution of Louis XVI” in 1793.
 

Today we observe similar tumultuous times and a changing climate. However this time the changing climate is not the result of a short-lived volcanic aftermath. The warming caused by the anthropogenic carbon-dioxide emissions  into earth´s atmosphere will continue for the next centuries. Some research has suggested that a warmer climate will fuel future conflicts. Droughts can cause water and food shortages in less industrialized nations. In 2010 drought in Russia and too wet weather in Europa caused a 20% loss of crops harvest, prices in response were raised on the international market by 40 to 70%, also due speculations. China, also suffering from a poor harvest, stocked crop, causing ulterior shortages.

The increased costs, widespread unemployment and misery lead to riots and demonstrations in many North African countries. The chaos lead in part to installments of  governments controlled by the military and in Syria (hit also by a drought from 2006 to 2010) the civil war is still going on. The civil wars in Africa and Near East caused mass migrations of refugees to the first world countries, Europe was not ready for the onrush, causing a political chaos. In response many right-winged parties, promising simple solutions like walls or travel bans, gained support in many European countries (U.K., France, Germany, Austria, Italy). Right-wing politics promised also simple solutions in the United States. The poor and middle class fears migration as this implies to share already limited resources. The rich class supports such fears as it distracts from the real causes (less than 3% of the population controls more than 50% of the global wealth).
Travel bans and suppressing research about climate change doesn´t solve problems but simply hides the truth. Already authoritarian systems like Russia or China seem also best fitted to deal with future climate change. Such systems can suppress disadvantageous news about climate change effects but also react faster to impending disasters. China, dealing with severe environmental problems due its rapid industrialization, planted millions of trees in governmental controlled projects or simply limited traffic in cities. Such projects would need more effort, time and especially support by citizens in democratic systems.
In times of supposed chaos, overwhelmed by the problems (real or faked), we demand for simple solutions, as authoritarian systems can quickly promise (if they really will hold the promise is another problem), but simple is not necessary the right way.

Non Sequitur by Wiley Miller

Bone and blood is the price of coal - Animals in Mines

"Humanity’s genius is to have always had a sense of its weakness. The physical energy and strength, with which nature insufficiently endowed humans, is found in animals that help them to discover new territories."
From the movie "Home" (2009)
 

Since prehistoric times humans searched for rocks and minerals hidden deep inside earth. First for silex and quartz, used for stone tools, later for metals and finally for coal and oil to fuel the industrial revolution.
 

In antiquity the work in mines was done by prisoners or slaves. In the middle ages miners became professional workers. The demand was so high that miners were members of a privileged social class, often freed from direct taxes, living in villages with own independent jurisdiction. The price for the privileges was nevertheless high. The work in the mines was dangerous, rock-fall and sudden flooding of the tunnels, wet and cold conditions for hours, poisoned air and dust causing sickness and death.
 
But not only humans, also animals had to suffer. In the middle ages animals, like horses, were not yet used directly in the mines, but to move large machines, like pumps, cranes and conveyor belts. Only after 1750 pit ponies were introduced for the first time in coal mines to pull mine tubs.

Fig.1. & 2. A horse as engine, image from Georgius Agricola "De re metallica libri XII" (1556). Apart horses or mules, in alpine regions also dogs were used to help in the transport of the ore, here carrying empty bags up the mountain.

Fig.3. A pit pony in a subterranean railway tunnel.

Apart infrastructure, animals played also a role in the security and hygiene of a mine. To detect poisonous and highly explosive methane-gas, called also grisú, miners relied on canary birds. As birds however have a poorly developed sense of smell they were more useful to detect carbon monoxide, as this gas would suffocate first the birds, warning so the miners.

Fig.4. Miners using a canary.

To control rats and mice in the Yorkshire mines terrier dogs were used, the Yorkshire was breed for size and agility, to catch rats even in the narrowest of tunnels and galleries.
 

Cats were used as living detectors. Able to see in near darkness and thanks to their keen hearing, entrapped miners could be more quickly found and may rescued in time.
 

Modern mines nowadays use powerful machinery and sensors have replaced the cats, but it´s still hard work. Also still in many less developed countries, working in small mines, humans and animals risk their health and lives to extract the precious metals, essential to run our modern electronic gadgets.
 

Famous physician Philippus Theophrastus Aureolus Bombastus von Hohenheim (1493-1541), better known as Paracelsus, interested both in mines and diseases, once wrote:

“...nothing good can be acquired without a price.“

Damned Souls and Fiery Oceans - Early Views Of Earth`s Core

"We know more about the stars high above our heads, than about earth just below our feet."
Leonardo da Vinci
 

There is some truth in da Vinci´s words, as for a long time the interior of earth was a mysterious place, supposedly the reign of demons and place of eternal damnation. Italian poet Dante Alighieri (1265-1321) imagined a core of ice, an allegoric image, far away from the sun and divine light where the damned souls are entrapped in eternal ice. 

German Jesuit Athanasius Kircher (1602–1680) imagined earth´s section in his "Mundus Subterraneus" (1664-1665) as crossed by veins of water and fire. The water would feed springs and rivers, the fire the volcanic mountains – but apart practical observations Kircher´s worldview was influenced also by religious-philosophical considerations, the two opposite elements water and fire united in a perfect creation.
 

Fig.1. from "Mundus Subterraneus", first edition published in 1664-1665.

Leonardo da Vinci´s (1452-1519) approach was more rational, even if inspired by the idea that earth worked a bit like a human body, just blood replaced by water. Water, so da Vinci, eroded, transported and deposited sediments, connecting mountains with the sea. He imagined earth filled by an immense underground ocean, sections of the superficial crust sinking into it would explain the formation of mountains.
 

Fig.2. Leonardo da Vinci´s speculative section of planet earth, from his private notes (Codex Leicester, 1510).
 

James Hutton (1726-1797) recognized the importance of magmatic rocks on earth. To explain the large quantities of volcanic rocks on earth´s surface and the energy needed to melt rocks, Plutonists proposed a molten interior, even if it is was not clear if molten rocks form most of earth or were to be found in only large magmatic chambers, distributed in the upper layers of earth.
 

Fig.3. Section of earth from Erasmus Darwin´s poetic-naturalistic work (1791), note the "unknown region supposed to consist of Lava kept in semifluid state by heat...[]".

French science-fiction author Jules Gabriel Verne (1828 - 1905) based his novel "A Journey to the Center of the Earth" (1864) on the science of his time. In his novel Verne uses the hollow conduit of the Icelandic volcano Snæfellsjökull to venture inside earth, an idea supported by the geologic models of volcanoes proposed at the time - a single or a series of magma chamber(s) with conduits connecting them to the surface. Geologists assumed that during an eruption the magma reservoir becomes empty and large voids and caverns were left behind.
 

Fig.4. Geological section, published in the book "Einführung in die Erdbeben- und Vulkankunde Süditaliens" (1914), shows the anatomy of a stratovolcano, with a main conduit, various lateral dikes and a large sill connected to the magma reservoir. 

The Spanish adaptation of Verne´s novel "The Fabulous Journey to the Center of the Earth"/ Where Time Began" (1976) summarizes best the problems geologists faced all this time:

"-Gentleman, the truth is that all our theories are just that, theories. None of us has the least idea of how the earth was really formed. Because the distance between the earths crust and its core is over 6.500 kilometres, and no men has ever descended to a depth of more than 3 miles. So it's obvious, we will never have a glimmer of true knowledge, until we are able to reach a depth of at least a 100 leagues.
 

- What's your opinion Professor Lindenbrook?
 

- Well gentlemen, at one point at least I agree with Professor Christophe, the materials of the geologists are not charts, chalk and chatter, but the earth itself. We should never know the truth, until we are able to make that journey, and see for ourselves."

To be continued...

Bibliography:
 

PARCELL, W.C. (2009): Signs and symbols in Kircher’s Mundus Subterraneus. In Rosenberg, G.D., ed., The Revolution in Geology from the Renaissance to the Enlightenment: Geological Society of America Memoir 203: 63-74

This 1783 Volcanic Eruption Changed The Course Of History

“The sun fades away, the land sinks into the sea,the bright stars  disappear from the sky,
as smoke and  fire  destroy  the world,
and the flames reach the sky.”
The End of the World according to the “Völuspa“, a collection of Icelandic myths compiled in the 13th century.

June 8, 1783 marks the beginning of a volcanic eruption that will change history…

The Four Layers of Earth

In a letter dated to March 30, 1759 the Italian mining engineer Giovanni Arduino (1714-1795) proposed to the physician and fossil collector Prof. Antonio Vallisnieri the subdivision of earth’s crust in various types, or layers, of rocks.

Based on his observations along the foothills of the Alps, Arduino recognized a stratigraphic column with four rock-layers: unstratified or poorly stratified crystalline rocks (or “Primary Rocks“, survived into the 20th century as “Paleozoic“ epoch), stratified rocks (“Secondary Rocks“, or “Mesozoic“), more recent, as yet unconsolidated, sediments (“Tertiary Rocks“) and finally all volcanic rocks.

Arduino used a section of rocks exposed in the Val d´Agno to explain his classification scheme. The numbers refer to the thickness of the strata, the letters to the description in the accompanying text. The extremely tattered state of the original drawing suggests that Arduino demonstrated it repeatedly to the many naturalists who visited him.

Bibliography:

VAI, G.B. (2007): A history of chronostratigraphy. Stratigraphy Vol.4 No. 2/3: 83-97

On the Art of Mineral Identification

Hardness is an important feature used for mineral identification, but it is not the only one. 

Fig.1. Lecture in mineralogy, from Bartholomäus Anglicus "Über die Eigenschaften der Dinge" (1390-1400), on the Characteristics of Things.
 
May the chemist Torbern Bergmann (1735-1784) was one of the first naturalist to discuss mineral-hardness, however, as he believed that clay is also a mineral, he assumed that hardness was strongly influenced by the humidity of the environment and therefore not very useful. In 1784 the geologist A.G. Werner published his textbook "Von den äußerlichen Kennzeichen der Fossilien" (The external characteristics of fossils; fossils as anything excavated from the ground) introducing six hardness-degrees that could be distinguished with simple tools, like a knife, a file or steel-tools, all things available to miners or amateur rock-hounds. Mineralogist René-Just Haüy (1743-1822) introduced also test-minerals, like calcite (Mohs Hardness 3) and quartz (Mohs Hardness 7) for hardness identification. Finally mineralogist Carl Friedrich Christian Mohs published the modern 10-degrees scale in 1822.

 

 

Fig.2. Hornblende (Moos in Passeier, South Tyrol).

The streak, the color of the mineral-powder, is mentioned already by Georg Pawer (1494-1555), better known as Georgius Agricola, in his books on mining techniques. Also Werner considers the streak one of the most important features, where Mohs considers both streak as color of the crystal equally important. However it was Werner to introduce a classification scheme for crystal colors, using terms like steel-gray and apple-green to describe the colors of minerals.
Curiously to get the powder the crystal had to be crushed or damaged, only in 1865 streak plates were introduced.
 
Specific weight was used already by Arabic scholars to distinguish gemstones from fake stones.

 

Fig.3. Apatite (Lodner, South Tyrol). 

Also the reactions of minerals with chemical solutions can be very important. A sort of marble was known already as "Bitterspat", "Murakalzit" and "marble tardum" by Carl von Linné (1707-1778). However in 1791 the French naturalist Deodatus Sylvain Guy de Tancrède greatet de Dolomieu (1750-1801) noted that this rock doesn´t react with acid like common limestone and limestone-marble does. He published this observation and later the Irish chemist Richard Kirwan identified and named the new mineral dolomite - a Ca-Mg-carbonate.

Fig.4. Dolomite from the Dolomites, South Tyrol.

Today many other features, like magnetism, luminescence and radioactivity are used to identify minerals. However until the 18th century only some hundred minerals were known, mostly ores or gemstones, and the described identification methods were more than appropriated for everyday use.

Bibliography:

KORTINIG, S. (1988): Der Strich. Der Aufschluss, Jhg. 39: 221-225
KORTINIG, S. (1988): Die Härte der Minerale. Der Aufschluss, Jhg. 39: 371-378
KORTINIG, S. (1988): Die Farbe und der Glanz der Minerale. Der Aufschluss, Jhg. 39: 295-299
KORTINIG, S. (1988): Die Dichte der Minerale. Der Aufschluss, Jhg. 39: 376-378
MÜCKE, A. (1988): Die Seiten für den Anfänger. Der Aufschluss, Jhg. 39: 35-38

Mineral Classification Made Easy - Mohs Hardness Scale

Talc – Gypsum – Calcite – Fluorite – Apatite – Feldspar – Quartz – Topaz – Corundum – Diamond -  “Mohs Scale of Mineral Hardness ” should be familiar to rock-hounds and earth-science students alike, as it lists common minerals in the order of the relative hardness (talc as the softest and diamond as the hardest mineral). Almost all  basic classification charts include this scale, as mineral hardness can be a quite useful criteria to identify unknown minerals and can be easily tested in the field (a steel blade corresponds to fluorite and a piece of glass to quartz).

Mohs scale  is appropriately named after the German mineralogist Carl Friedrich Christian Mohs (lithograph by Joseph Kriehuber, 1832), born January 29, 1773 in Gernrode (at the time located in the principality of Anhalt-Bernburg), son of a middle-class family.

After school he worked in his father’s business as merchant, but in 1796 he went to the University of Halle to study  mathematics, physics and chemistry. He continued his studies at the famous Royal Saxon Mining Academy of Freiberg, where he studied under the even more famous geologist Abraham Gottlob Werner. Werner had published in 1787 a “Kurze Klassifikation und Beschreibung der verschiedenen Gesteinsarten” (Short classification and description of the various rock types), a classification guide that used – unusual at a time when most rocks were classified based on the complex rock-chemistry - easily recognizable features (like color)  to identify minerals and rocks.

Mohs was impressed by the approach of Werner and in 1804 published himself a “student-friendly” classification chart for minerals, based on his experience in the mining district of the Harz and as consultant for wealthy mineral-collectors.
In the work”"Über die oryktognostische Classification nebst Versuchen eines auf blossen äußeren Kennzeichen gegründeten Mineraliensystems” (The genetic-geological classification and an attempt to introduce a mineral-system based on superficial properties) Mohs combines various physical properties of minerals (like color, hardness an density) with 6 classes of crystal shapes  (in part in use even today) to identify 183 different minerals.

Fig.2. and 3. Specimens of Quartz (Mohs hardness 7) and Calcite (Mohs hardness 3), both minerals are common and can be very similar in shape and color, however they are easily recognizable by the different hardness, calcite can be scratched with a knife blade, quartz not.

After 1812, now as a professor in the Austrian city of Graz, he continued to improve his mineral classification scheme and to publish guidelines for mineral identification. In 1818 he succeeded Werner and became professor in Freiberg and between 1822-1824 Mohs finally published his famous hardness scale in the book  “Grund-Riß der Mineralogie” (Essentials of Mineralogy).

 
Bibliography:
 
HÖLDER, H. (1989): Kurze Geschichte der Geologie und Paläontologie – Ein Lesebuch. Springer Verlag, Heidlberg: 243
WAGENBRETH, O.(1999): Geschichte der Geologie Deutschland. Georg Thieme Verlag: 264

From the Contracting Earth to early Supercontinents

“What are they? Creations of mind?- 
The mind can make Substance, and people planets of its own  
With beings brighter than have been, and give  
A breath to forms which can outlive all flesh.”
“The Dream“, Lord Byron (1788-1824)

Already when the first maps of America were published (1507 and after), geographers and naturalists alike noted the similar shape of the west-coast of Africa and the east-coast of South America.

In 1620 the English philosopher Francis Bacon claimed in his “Novum Organum” that “it’s more then a curiosity”. In 1658 the cleric Francois Placet published a small booklet entitled “The break up of large and small world’s, as being demonstrated that America was connected before the flood with the other parts of the world.” He argued that the two continents were once connected by the continent of “Atlantis”, submerged and lost forever during the biblical flood.

The idea of a flood to explain the shape of continents will remain very popular for the next 250 years.

Fig.1. Illustration from Thomas Burnet´s book “The Sacred Theory of the Earth“, published in 1684, where he tries to explain the shapes of the continents by the biblical flood. The homogenous primordial crust of earth is shattered (first drawing) releasing water from the underground. This water covers the entire planet (second drawing) and finally flows back in the fissures, leaving behind fragments of the crust that now forms the modern islands and continents (last drawing).

The great French palaeontologist Buffon in his “Les Epoques de la Nature” (1717) not only addresses the age of earth, but also speculates about a former land bridge connecting Ireland and America to explain the distribution of fossil shells found on both sides of the Atlantic Ocean.

The American president (of the Academy and College of Philadelphia) and naturalist Benjamin Franklin explained marine fossils found on mountains in a letter to French geologist Abbé J. L. Giraud-Soulavie in 1782 as follows:

“Such changes in the superficial parts of the globe seemed to me unlikely to happen if the earth were solid to the center. I therefore imagined that the internal parts might be a fluid more dense, and of greater specific gravity than any of the solids we are acquainted with, which therefore might swim in or upon that fluid. Thus the surface of the earth would be a shell, capable of being broken and disordered by the violent movements of the fluid on which it rested.“

The great German naturalist and geographer Alexander von Humboldt explored South America in 1799-1804 and observed that the similitudes between the two coastlines were not only restricted to a morphological pattern, but also to the geological features: mountain ranges that seemed to end on one continent continued on the other, the Brazilian highland is similar to the landscape of the Congo, the Amazonian basin has it’s counterpart in the lowlands of Guinea, the mountain ranges of North America are – geologically – very similar to the old European mountains and rocks in Mexico resemble those found in Ireland.

Fig.2. Columnar Jointing in the basalts of Regla, Mexico, as depicted in Alexander von Humboldts (1810) “Pittoreske Ansichten der Cordilleren und Monumente amerikanischer Völker.” (image in public domain), the accompanying text explains: “The basalts of Regla, which are presented on this copper plate, are an incontrovertible proof of this identity of forms, which is noted on the rocks of different climates. Travelled mineralogist need only to look at this drawing to recognize the basalt forms in Vivarais, in the Euganean Mountains or in the foothills of Antrim, in Ireland. The smallest coincidences observed in the European rock-pillars are also found in this group of Mexican basalts. Such a great analogy let us assume a similar principle of formation acting under all climates in various temporal epochs, the basalts covered by compact limestone and clay-slate must be of different age than those who are resting on layers of coal and boulders.”

But even Humboldt still argued that the Atlantic Ocean represents a large and ancient river bed, flooded subsequently by the biblical catastrophe.

The French zoologist Jean-Baptiste Lamarck developed a surprisingly new hypothesis. To explain the discovery of fossil marine animals on dry land he proposed that the continents “move” slowly around the globe in a very peculiar manner. The eastern coastlines of the single continents are eroded by the sea, but in the same time new sediments were deposited on the western coasts, so the continents apparently move around the globe and the sea becomes land.
Unfortunately, also for the lack of evidence for his theory, Lamarck was not able to find a publisher for his “Hydrogéologie” and printed in 1802 on his own behalf 1.025 copies, but only a small number of books were sold.

In the early 19th century another hypothesis was proposed to explain the shape of Earth: the Contracting Earth theory formulated by the American geologist James Dwigth Dana explained mountains and continents as products of a cooling and subsequently shrinking earth. Like an old and dry apple the shrinking surface of earth would develop fissures (basins) and wrinkles (mountains).

Austrian Geologist Eduard Suess published in his multi-volume work “Das Antlitz der Erde” (1883-1909) this hand coloured map, showing the supposed remains of the primordial continents – preserved “cores of crust” surrounded by younger basins today filled with oceans. Curiously he suggested also that the deep-sea trenches, found along the borders of the Pacific, are zones where the ocean floor was pushed under the continents (!).

Fig.3. Hand coloured map showing the primordial continent -”cores” according to the Austrian geologist Eduard Suess, published in “Das Antlitz der Erde” (The Face of the Earth) 1883 to 1909 (image in public domain).

But the Contracting Earth theory couldn’t explain the irregular distribution of mountains on earth and why there are regions with strong tectonic movements and earthquakes and also “quiet” areas. According to this theory, such features and events should to be distributed randomly on the surface of a homogenous cooling and shrinking planet.

Already in 1858 the French naturalist Antonio Snider-Pellegrini (1802–1885) published a reconstruction of America and Africa forming a single continent on a planet with a fixed volume. But Snider-Pellegrini couldn’t propose a convincing mechanism, apart the great flood described in the Bible, to explain the forces needed to move entire continents.

Fig.4. This 1858 reconstruction by Antonio Snider-Pellegrini is the first map showing a former supercontinent.

Bibliography:

FRISCH, W.; MESCHEDE, M. & BLAKEY, R. (2011): Plate Tectonics – Continental Drift and Mountain Building. Springer-Publisher: 212
MILLER, R. & ATWATER, T. (1983): Continents in Collision. Time-life books, Amsterdam: 176