1886.] some of its Apparent Causes. 37 
from the Pacific, a period of dessication set in throughout the great 
basin between the Rocky mountains and Sierra Nevada, and exten- 
sive rainless districts resulted, But even then there were alter- 
nate wet and dry cycles throughout the early Quaternary. Great 
Salt Lake, from being a vast body of fresh water, became a shal- 
low brine pool; the sources of the Colorado, Columbia and their 
tributaries likewise partially dried up. 
Finally, the Glacial epoch came in, the glaciers invaded North- 
eastern America; these on the one hand, and the great elevation 
of the western plateau, seem to have been the causes which re- 
moved the Pliocene fauna; which removal was, geologically speak- 
ing, comparatively sudden. 
Either at the end of the Pliocene or beginning of the Quater- 
nary, as seen by the bones in the Port Kennedy cavern described 
by Professor Cope, there was a singular mixture of what we now 
regard as tropical and temperate forms living so far north as Penn- 
sylvania; with the tapir, peccary, Mylodon, Megalonyx, Castor- 
oides and sabre-toothed tiger, were apparently associated the deer, 
bison, horse, porcupine, raccoon, dog, weasel and smaller mam- 
mals. The fauna was in part extinguished by the glacial cold, 
Port Kennedy being situated a little south of the edge of the great 
glacier. 
The result of a change of climate was a change in the nature 
of the forests ; the tapir and peccary were forced to migrate south- 
ward ; the colossal sloth and sabre-tooth tiger died outright; the 
Castoroides, horse and mastodon lingered through the Glacial 
epoch, their remains being found at the bottom of swamps, but 
above the glacial and river drift; while the deer, bison, raccoon, 
dog or wolf, and other forms survived with unimpaired vigor and 
became adapted to a lower climate, forming the typical members 
of the north temperate fauna of America. | 
Farther south, in the river gravels and caves of the Middle and 
Southern States, are found the bones of the great sloths, Megathe- 
rium, Megalonynx and Mylodon, the American lion and bear ; 
these were possibly swept out of existence by the cooler winters 
of the Mississippi valley, which was free from ice, but probably had 
from their proximity to the great glaciers a lower climate than in 
Pliocene times. 
Professor Cope remarks: “ Since the Eocene, the mammalian 
fauna of the northern hemisphere has diminished in number of 
