118 ANNALS NEW YORK ACADEMY OF SCIENCES 



the bottom. From the lower shale, a biyozoan and brachiopod fauna was 

 obtained, which Professor Schuchert assigned to the Burlington-Keokuk 

 horizon. The upper limit of the Great Blue limestone merges gradually 

 into the Upper Intercalated series, wdiich, with its frequent alternations 

 of siliceous and calcareous beds, is in sharp contrast with the heavy blue 

 layers of the Great Blue limestone. Between these two formations, 

 Schuchert places the division between the Carboniferous and Mississip- 

 pian. The Mississippian in the Oquirrhs is thus made somewhat over 

 6000 feet, and the upper division, counting the Weber quartzite exposed 

 at Bingham and over a large area to the north, between 15,000 and 

 18,000 feet. 



To facilitate the discussion and bring out the relationships which exist 

 among the Carboniferous formations of the Oquirrh, Wasatch and Uinta 

 mountains, columnar sections from these three ranges taken in an ap- 

 proximate east-west line through the Cottonwood district have been 

 drawn side by side in Fig. 4. The distance between Mercur and Big 

 Cottonwood Canyon is about equal to the distance from Big Cottonwood 

 to the western Uintas, being in the neighborhood of thirty-five miles. 



The much greater development of Mississippian and Pennsylvania 

 strata in the Oquirrh Mountains is seen at a glance. The corresponding 

 parts are indicated by the dotted lines. It becomes apparent at once that 

 the unconformities shown in the Wasatch and Uinta sections represent a 

 long interval of erosion. Farther to the east, in Colorado, this same 

 unconformity has been reported between the Mississippian and Pennsyl- 

 vanian formations, and the same explanation no doubt applies there as 

 well. It seems reasonable to suppose that the Mississippian was repre- 

 sented by much thicker formations in these sections at the beginning of 

 Pennsylvanian time than is shown at present. The Great Blue limestone 

 was very probably represented in them all, but just when the area of the 

 Wasatch and eastward into Colorado was lifted and exposed to erosion 

 cannot be definitely stated. It was probably toward tbe end of Great 

 Blue time. During the long period of erosion which followed, most of 

 the Mississippian limestone w^as worn away and transported elsewhere to 

 be deposited as calcareous mud or, if dissolved, remain in solution in the 

 sea water. The new shore line receded westward until it came to occupy 

 some position between the Wasatch and Oquirrh mountains. Here it 

 seems to have remained for a long time, as we may judge from the nature 

 of the great deposits which formed in the Oquirrh Mountain area. 



Above the Great Blue limestone, we have the Upper Intercalated series, 

 which on the Mercur side of the divide is from 5000 to 6000 feet thick, 

 but it continues east of the divide and may be as much as 10,000 feet in 



