Science blogger Greg Laden writes, "Everyone knows that Darwin was a biologist, and in many ways he was the first prominent modern biologist. Though Darwin scholars know this, many people do not realize that he was also a geologist."
But was he a good one?
YEC geologist Steve Austin visited the site of Darwin's camp on the Santa Cruz River in Argentina, interpreted by Darwin to be the result of slow erosion over a long time: "The river, though it has so little power in transporting even inconsiderable fragments, yet in the lapse of ages might produce by its gradual erosion an effect of which it is difficult to judge the amount."
However, as Austin shows in "Darwin's First Wrong Turn," (http://www.icr.org/article/darwins-first-wrong-turn/), Darwin seriously misinterpreted the geology. Basalt cliffs and boulders high above the valley floor actually mark the spillway of what is probably a glacial outburst flood.
The Santa Cruz River itself is seriously underfit for its channel, highlighted in orange in the image above, which originates in the glaciers and glacial lakes of the mountains to the west. The actual river follows the trace of the black lines, so you can see the contrast between the spillway and the current river channel.
Austin notes that Darwin "...saw the structure of the present valley and understood it to have been formed by the continued slow action of the modern river during the lapse of great geologic ages. Later, Darwin revisited the bogus methodology when he assumed that beaks of finches on the Galapagos were derived slowly during geologic ages from a common bird by the cumulative process called natural selection. ... Darwin was in error about the Santa Cruz River valley. What if young Darwin had correctly interpreted the colossal flood evidences within the valley? Would he have later entertained that biological extrapolation called biological evolution? ... It is evident that Darwin became a committed geological evolutionist before he became a biological evolutionist. Camp Darwin marks this young naturalist’s first scientific wrong turn."