Alex L. Du Toit
To understand something about Alex du Toit’s work in continental drift when it was not accepted by science, it would help to talk a little about his predecessor in that area of study, Alfred Wegener. Wegener was a German meteorologist, astronomer and geophysicist who had noticed something that would get him in big trouble.
The mountains that run from east to west across South Africa seemed to link with the range near Buenos Aires in Argentina. Fossils of certain small reptiles and seed ferns of the same age were found in very similar strata separated from one another by a vast ocean. South America and Africa seemed to fit along their Atlantic coasts as precisely as if one day a giant had come along and pulled them apart along a seam. Surely there was a reason; it could not be a coincidence. Wegener felt that the continents had moved across the face of the earth over time and there had been at one time one giant continent that split up. His 1915 book The Origin of the Continents and Oceans was brilliant, but he was too far ahead of his time. He could present no cause for continental drift. We now know the ocean floor crust not only spreads but also is drawn back into the mantle at various points, causing continents to collide and tear. Back in 1915 this was only an idea, and a wild one at that. The favoured idea behind mountain building was something that involved heavy portions of a continental shelf crust, weighed down by thick offshore sediments, being pushed down. This was thought to cause lighter sections to bounce up, for lack of a better word. Scientists felt this was because of the pressure of contraction and adjustments inside the earth’s interior mantle. The interior was thought to be a semiliquid. It is true that crustal adjustment does occur and that there is a state of equilibrium between the crust and mantle. But the mantle is solid. Some liquefaction occurs in the crust and upper mantle when pressure is released during sea floor spreading and volcanic eruption.
If fossil land plants and animals from ancient South America’s Atlantic coast were likewise found as fossils in western South Africa’s western coastal rocks, the scientists felt it had to be because of land bridges. Evidence for these land bridges was lacking, but it was the only answer. The continents did not roam around, bumping into one another! The Atlantic sea floor had not been explored much during that time. The existence of a Mid-Atlantic Ridge was not certain. Wegener was told by his fellow scientists to return to his weather instruments and lecturing.
South African geologist Alexander du Toit fared better than Wegener. He was not one to shy away from controversial ideas either. Hailing from Rondebosch, he graduated from South Africa College (now the University of Cape Town) and went to Scotland to earn another degree in mining engineering in 1899 from the Royal Technical College in Glasgow. While in Scotland he met and married Adelaide Walker. The young couple went back to South Africa in 1903 and du Toit signed up with the Geological Commission of the Cape of Good Hope. They had one child, Alexander Robert. Adelaide died just a few years later, and du Toit married Evelyn Harvey.He set to work creating field sheets and geological maps of parts of the Cape Town area and the area between Herschel and Cala. The geologist covered thousands of kilometres, using a plane table conveyed on a donkey cart hitched to a bicycle. His wife and son helped him in the field. Alex du Toit ceased field work for a time, went back to Glasgow for his Ph.D. and worked up and down the Indian Ocean coast, mapping the geological formations. He served as hydrogeologist for the South African forces during World War I and by the end of the war was president of the Geological Society of South Africa.Alexander du Toit served the Union Irrigation Department from the early 1920s to 1927 and from 1927 to 1941 was a consulting geologist for De Beers Consolidated Mines. This was his primary focus for most of his career. He now had the reputation needed to be able to secure a grant from the Carnegie Institute in the 1920s to compare the geology of South Africa and South America. He was amazed to be awarded the Murchison Medal by his fellow geologists in 1933. The trip to South America led to a book, Our Wandering Continents, in 1937. He dedicated it to Alfred Wegener. Many of du Toit’s fellow scientists disliked his flowery descriptions of earth processes and complained that it made the book a bit hard to follow, but they could not deny that he was seeing something in his radioisotope dating studies of the rocks of the two continents that could have profound implications. Instead of a simple super continent, du Toit reconstructed some continents at the South Pole and placed another group near the equator. We now know these ancient continents as Gondwanaland and Laurasia, and the sea between them as the Tethys Sea. For du Toit, the idea of a network of land bridges was “fundamentally unsound”.
The discovery of palaeomagnetism and advancements in surveys of the ocean floor were necessary steps in the development of ideas started by Wegener and du Toit.
Paleomagnetism simply means that in molten lava or in magma just under the surface, or in cool soft sediments, magnetic mineral particleswill align themselves with the Earth’s magnetic field. When the hot rock cools and when the sediment becomes stone, the rocks become a kind of record of where that portion of the continent was oriented relative to the North and South Pole of the day. Pretty good for a mere rock! The deviations in the alignment of these paleomagnetic particles from the current direction of the Earth’s magnetic north and south poles shows that the continents have not been sitting still.
Physicist Patrick Blackett in England developed a sensitive device called the astatic magnetometer in 1948. Now it was possible to detect very weak magnetic fields in rock. Earlier instruments simply were inadequate to detect this property. This enabled researchers to conduct paleomagnetic studies of a larger variety of rocks of the crust. Alex du Toit heard of Blackett’s work but did not live long enough to see this widely used to prove his still-unpopular notions of continental drift. He died in February 1948 in Cape Town.
Icelandic Mid-Atlantic Ridge volcanoes
Nevertheless, it took the discovery of the Mid Atlantic Ridge in the 1950s to encourage scientists to abandon most of the old notions. The largest single geologic feature on earth, this ridge system was one huge surprise. Molten magma from beneath the crust wells up constantly in the center. It then cools and is pushed away from the Ridge’s flanks. The basalt rock of the ocean floor is noticeably younger than the rock farther away.
Iceland
Iceland gives us a chance to see the Ridge on dry land. Had he lived another decade, Alex du Toit would have been very excited to see this discovery in the news and the scientific journals. This was the mechanism for the separation of Africa and South America!
Alexander du Toit is not a household name; but one of my sister’s geology professors, in referring to the earth as a “dynamic planet”, frequently brought up du Toit’s studies as an illustration.
Alex L. du Toit’s hand drawn map