GREAT SALT LAKE BASIN 
103 
record of a past humid period in the basin of the Great Salt 
Lake in Utah. All round the present lake we find a most 
interesting series of terraces at varying heights, which clearly 
represent ancient shore-lines. It has thus been established 
that in Pleistocene times, during its greatest development, 
the lake had the enormous area of more than 19,000 square 
miles, that is, nearly the size of Lake Michigan, with a depth 
of about 1,000 feet. This ancient “ Lake Bonneville,” as it 
has been called, has since been greatly reduced in size by tbe 
slowly increasing aridity of the country. Its diminutive 
descendant, the Great Salt Lake, is rapidly drying up, its 
average depth being only twenty feet. Other large fresh-water 
lakes existed in the Great Basin during the Glacial Epoch. 
Sometimes it is customary to include the western Sierra 
Nevada and Cascade Mountains under the term “ Rocky 
Mountains.” Asa Gray and Sir Joseph Hooker have even 
added to this area that of the Great Basin in their account 
of the Rocky Mountain flora. More recently the distinctive¬ 
ness of these two mountain systems is being more generally 
recognised. The forests of the Rocky Mountains are dis¬ 
tinguished from those of the eastern States by the prevalence 
of the pyramidal evergreen conifers, whereas in the east the 
trees are round-headed and mostly deciduous. The endemic 
flora, consisting of thirty-three per cent, of all the plants 
found in the Rocky Mountains, forms a prominent element.* 
We have noticed that some of the alpine plants inhabiting 
the White Mountains are unknown in western America, for 
instance, Diapensia lapponica and Loiseleuria procumbens. 
On the other hand, a large number of the alpine Rocky Moun¬ 
tain species do not occur in the east, whereas a few, such as 
Rhododendron lapponicum, Arctostaphylos alpina, Rubus 
chamaemorus and Veronica alpina, are common to both, point¬ 
ing to the great antiquity of this element in the flora.f 
Many of the plants occur also in Asia; others are closely 
related to arctic-alpine species. Most of the endemic element 
of the Rocky Mountain flora has clearly been derived from that 
* Gray, A., and J. D. Hooker, “Vegetation des Eocky Mountain 
Gebietes,” p. 267. 
t Eydberg, P. A., “Composition of Eocky Mountain Flora,” p. 870. 
