>64 REV. PROF. G. F. WRIGHT, ON THE INFLUENCE OF THE 
affecting the struggle for life between competing species. In 
the advance of the glacial ice in North America, for instance, 
animals and plants were driven southwards from an area of 
4,000,000 square miles ; the southern border of which reached 
in Illinois nearly to the junction of the Ohio with the 
Mississippi River in latitude 38°. 
It is impossible to over-estimate the strenuousness of the 
•struggle for existence which was set up in the restricted 
area in the southern part of the United States and Northern 
Mexico, lying between the glacial conditions in the north and 
the tropical conditions which prevented migrations southward 
across Central America. Then, again, upon the amelioration of 
the northern climate and the re-opening of the northern region 
to the animals which had survived the former changes of 
■conditions, many of them re-occupied the ground, and began 
the struggle with new conditions, to which some of them, 
•especially the mammoth, in due time succumbed. 
Local floods of enormous extent during the closing stages of 
the Glacial Epoch seem to have been connected in a marked 
■degree with the destruction of both man and animals which 
took place during this epoch. The remains of man which have 
been found within the last few years in the loess of the Missouri 
Yalley (referred to above) are connected with annual floods 
which can be definitely proved to have risen 200 feet. These 
floods were occasioned by the rapid melting of the ice in the 
upper part of the valley, and the gorging of the w^ater lower 
down, producing annually for a while in the latter part of each 
summer a temporary lake 1,000 miles long and from 70 to 80 
miles wide. Similar conditions existed in the valley ot the 
Ohio and down the Mississippi as far as Vicksburg. 
At this time the depression which now contains Great Salt 
Lake in Utah was filled up to a depth of 1,000 feet, and covered 
an area of 20,000 square miles, ten times that of the present 
lake. When at last this glacial lake surmounted its barriers 
.and broke over into the Snake River Yalley, it quickly brushed 
away 350 feet of the mud barrier which restrained it, and that 
depth of water rushed down the valley in a torrent as large 
as Niagara for 25 years* The results of this are incom- 
prehensible. 
Likewise in Southern Russia, if the loess covering that region 
is connected with the same stage of the glacial recession, man 
* See Gilbert’s Report on Lake Bonneville , U.S. Geological Survey. A 
summary is given in my Man and the Glacial Period , New York, 1900. 
