"We slowly recognized this as the level on which all our explorations were to be made. The giant trunks of fossilized trees began to appear -- trees that were borne down the rivers from the great forests of the south, their petrified trunks, from thirty to seventy feet in length, protruding from the sand, which was an auspicious sign of the proximity of the remains of quadrupeds, for both were washed down together. Remains of crocodiles, also, and of great turtles, began to be seen, and we were convinced that we were in the very fossil-bearing tier itself."
Osborn, HF. 1907. The Century Magazine (74). 'Hunting the ancestral elephant in the Fayûm desert: Discoveries of the recent African expedition of the American Museum of Natural History.'