PALEOZOIC. 55 



the Paleozoic section of the Wasatch Range, as determined by the geolo- 

 gists of the Fortieth Parallel and which was considered by them as the key- 

 section of the Rocky Mountain region, and that of the Mosquito Range. 



In the former the Paleozoic series has a thickness of about thirty thou- 

 sand feet and is characterized by two great silicious series, the Cambrian 

 at its base and the Weber Quartzites in the middle of the Carboniferous. 

 The former had a thickness of about twelve thousand feet and was followed 

 by 1,000 feet of Silurian limestone, which was again succeeded by quartz- 

 ites and sandstones of equal thickness ; this was followed by a great lime- 

 stone formation of a maximum thickness of 7,000 feet, in the lower portion 

 of which were found Devonian and Waverly forms, the main body of the 

 limestone being, however, characterized by fossils of Carboniferous age. 

 The coarse sandstones of the Weber series, which were deposited over this 

 limestone, had a thickness in the Wasatch of about six thousand feet, and 

 were succeeded at the close of the Carboniferous by alternating silicious, 

 calcareous, and argillaceous beds. Followed eastward along the forty-first 

 parallel, the whole Paleozoic series thins out rapidly, and in the Laramie 

 hills, on the meridian of the Colorado or Front Range, seems to be rep- 

 resented by a thickness of only 1,500 feet of rocks, though the exposures 

 are not sufficiently good to render it certain that the entire series is here 

 exposed. 



In the Mosquito Range the Paleozoic series has a maximum thickness 

 of less than five thousand feet. The Cambrian is represented by quartzites, 

 passing gradually upwards into calcareous shales, with limestones of prob- 

 able Silurian age above, the aggregate thickness of the two being about 

 four hundred feet. Above these limestones, and separated from them by a 

 thin bed of quartzite, is the Blue, or ore-bearing, limestone, about two hun- 

 dred feet in thickness, in which only Carboniferous forms have yet been 

 found. This is succeeded by a relatively large development of silicious 

 material, consisting mainly of coarse sandstones and conglomerates, corre- 

 sponding lithologically to the Weber series, which passes upward into beds 

 containing a greater or less development of limestone, with sandstones and 

 shales, and which has been provisorily designated the Upper Coal Measures. 



