GILBERT ON THE GLACIAL EPOCH IN THE "GREAT BASIN." 211 
the cliff topography has prevailed in that region for a long time. There are 
evidences also that there were canons here before the present canons were 
carved. The* facts in relation to this matter can be better stated when we 
come to discuss the geology of the region. 
Mr. G. K. Gilbert, a geologist of Lieutenant Wheeler's corps, in a paper 
communicated to the Philosophical Society of Washington, in 1873, deduced 
a similar conclusion from an independent series of facts observed in Western 
Utah. The basin of Great Salt Lake, a portion of what Fremont designated 
the " Great Basin," has now so dry a climate that its waters gather in its 
lowest parts and evaporate and have no outlet to the sea. In a former 
period, however, there was more rain, the valley was filled with water to its 
brim, and in place of the Salt Lake Desert, there was a broad and deep 
fresh lake, discharging its surplus into the Columbia River. The epoch of 
this lake Mr. Gilbert finds reason to consider identical with the Glacial 
Epoch, and it was of limited duration. Among its vestiges are deposits of 
fossiliferous marl, which are conspicuously contrasted with the gravels and 
sand that now slowly accumulate in the. same region, borne by the intermit 
tent streams that descend from the mountains. Where the beds are super 
posed, the marls testify to a moist climate and the gravels to a climate so 
dry that the basin was never filled with water. But above the marls are 
found only scattered and thin deposits of gravel, while below them the 
gravel beds are omnipresent and of great depth, and hence it was reasoned 
that the arid period that preceded the Glacial Epoch was many times longer 
than that which has followed it. 
Even during the Glacial Epoch, Mr. Gilbert considers that "the Atlantic 
slope", and the region of the Great Basin, were contrasted in climate, just as 
now. The general causes that covered the humid east with a mantle of ice, 
sufficed, in the arid west, only to flood the valleys with fresh water, and send 
a few ice streams down the highest mountain gorges."* 
RECORDS OF MORE ANCIENT LANDS. 
The summit of the Kaibab Plateau is more than six thousand feet above 
the river, and I have already mentioned that the summit of the plateau is 
also the summit of rocks of Carboniferous Age. These beds are about three 
* Bulletin Phil. Soc.. Washington, 46th meeting, April 26, 1873. 
