Grand geological theories

geological cross-sections
One of Darwin's geological cross-sections through the Andes.  CUL DAR 44, f. 33

From his personal observations of the series of violent natural events, fossilised trees and other evidence, Darwin was attempting to visualise the geological history of the entire sub-continent of South America, testing his field observations against the competing geological theories of the time and, increasingly, constructing his own grand concepts. He developed his own interpretation of the Earth’s crust as huge sheets of rock – a similar concept to modern tectonic plates – that rose and fell as the molten material beneath heated and cooled, expanded and collapsed.  He also began to construct a series of geological cross-sections and these are amongst the most visually striking objects of Darwin’s surviving papers from the Beagle voyage. Hand-coloured, they range in size from 15cm to nearly 2m in width, and were pieced together from individual strips of paper and were based on the surface observations he made and the mineral samples he collected.
Travelling on from South America and crossing back half way round the world, Darwin started to apply this theory on a global scale. In his Red Notebook begun at sea in 1836, he jotted notes for himself for future publications, concluding that the ‘Geology of whole world will turn out simple’.