186 HSUCIBIL, (Ca LOS SVFILIL 
concave on the west, the longer diameter of the now truncated 
dome is 160 miles and its shorter diameter about 50 miles. At 
the south this uplift merges with another of similar character 
which trends more nearly east and west and has been deeply eroded. 
Its central mass of weathered granite forms the Wind River 
Mountains. Mountains having the same structure, extend south- 
ward into Colorado, and form several ranges designated by Powell 
as the Park Mountains. Each of these dome-like uplifts of 
Wyoming and Colorado has been deeply eroded, and broad cen- 
tral cores of granite exposed and sculptured into bold topographic 
forms. Sections through the mountains of Colorado from east 
to west, published in the “ Atlas of Colorado,” by Hayden, and 
the atlas accompanying the reports of the Fortieth Parallel Sur- 
vey, show great central masses of what is termed metamorphic 
granite. On the flanks of these central masses the sedimentary 
strata underlying the adjacent plains, are sharply upturned. In 
many instances the central granitic cores are from 20 to 30 and 
even 50 to 60 or more miles across. | 
These dome-like arches are clearly not anticlinical folds; 
although, that such was their origin has frequently been stated. 
Nothing in the Appalachian or other similar ranges, formed by 
the crumpling of stratified beds by lateral compression, cor- 
responds with them. Experiments with plastic material in illus- 
tration of the formation of anticlines and synclines, do not 
suggest that such broad, simple arches surrounded by horizontal 
strata can be produced in the same manner. These great upward 
bulges are similar to the Black Hills dome, the only conspicuous 
difference being that they are much elongated. If we arrange 
in a series, cross sections of the Black Hills, Big Horn, and 
Wind River Mountains and of several of the ranges included in 
the Park Mountains, it will be seen that a single type of uplift is 
shown in all cases. The same fact will appear also if restorations 
of the various domes as they would appear had there been no 
erosion, are placed side by side. That several of the more 
prominent ranges of Wyoming and eastern Colorado are of one 
type, was recognized by Hayden, who considers them, however, 
