GEEAT 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 the 

 slowly increasing aridity of the country. Its diminutive 

 descendant, the Great Salt Lake, is rapidly drying up, ita 

 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 Kocky 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 thk plants 

 found in the Eocky 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 Eocky 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. 



