REVIEWS AND BOOK NOTICES. 729 
the deposition of these lignitic strata began during the latter por- 
tion of the Cretaceous period, and continued on into Tertiary 
times. 3 
The origin of the Salt Lake valley, of which the remarkable 
Wahsatch Range forms the eastern boundary, seems due to a long 
continued erosion of a series of mountain chains spread over this 
area and resulting from a crumpling or folding of the earth’s crust. 
“It is most probable that at a comparatively modern period the 
vast area between the Wahsatch Mountains on the east and the 
Sierra Nevada on the west was one great lake, the mountains 
rising up as islands in this vast inland sea. The lakes, large and 
small, which we find scattered over the basin at the present time, 
are only remnants of this former sea.” Out of the flanks of these 
wrinkles in the earth’s crust, cations, with nearly vertical walls 1,000 
to 2,000 feet high, have been carved by atmospheric agencies, such 
as ice, frost and water. ‘The valleys between these folds or ridges 
are synclinals, which have been deepened by erosion. The is- 
lands in Salt Lake are only the crests of these folds, while the 
waters occupy the synclinal valleys; and this remnant illustrates, 
on a sinall seale, the scenic beauty of the great inland sea when it 
extended over the entire basin.” 
Farther north in the Yellowstone valley are magnificent speci- 
mens of canons whose mountain walls are formed of volcanic con- 
glomerate 1,000 feet in thickness. Such a valley of erosion is 
represented by Fig. 176. In the mountains at the source of the 
East and Yellowstone rivers these conglomerates are sometimes 
4,000 or 5,000 feet thick. These beds are supposed to have been 
“thrown out by volcanoes into the surrounding waters much as 
similar materials are injected from modern volcanoes at the present 
time.” As these beds are horizontal and regularly stratified from 
base to summit, Prof. Hayden concludes “that at a comparatively 
modern date, the waters so covered these mountain ranges of the 
northwest, that not even the summits of the loftiest peaks were 
above the surface. It is barely possible that we might make an 
exception in the case of the Grand Tétons. We may suppose 
that the materials were supplied from the numberless volcanic fis- 
sures in unlimited quantities in a comparatively brief space of 
time ; but the period which would be required for the waters to ar- 
range this matter in the remarkably uniform and compact series of 
strata which we find at the present time must have been great. 
