STANTON.] 



NEW MEXICO AND COLORADO. 33 



Colorado formation is still mainly composed of dark clay shales, though 

 there are occasionally thin intercalations of sandstone. A section on 

 Gunnison river, opposite Roubideau's creek, described by Dr. Peale. 1 

 which shows the general character well, is as follows: 



Feet. 



1. Slialy sandstones, with interlaminated argillaceous beds, extending from) 



the top of the bluif on the river to the base of the first bluff north of ] 

 the river. The beds are for the most part concealed \ 175 



2. Coarse yellow sandstone -w ith calcite J 



3. Gray laminated sandstone J 



4. Thin laminae of grayish sandstone shales, with fine black argillaceous shales, 



gypsiferous and calcareous, containing Inoceramus, Os'rea lugubris (Con- 

 rad), and other Cretaceous fossils Viol 



5. Yellowish sandstone shales, with quantities of Inoceramus and Ostrea espec- 



ially abundant near the top, where there is a layer of black shales 40 



6. Black argillaceous shales, partly concealed by debris 38 



7. Coarse yellow, gypsiferous, and calcareous sandstones, with layer at top, 



breaking into pencil-like pieces one to two inches long and an eighth of 



an inch in thickness 50|- 



8. Sandstone shales ) . 



9. Fine black argillaceous shales \ 



10. Coarse yellow calcareous sandstone, resembling that described under No. 7. 1 



11. Fine black argillaceous shales, with bands of sandstone (fossiliferous), spe- 



cies of Inoceramus and Ostrea 36 



12. Hard gray sandstone 1 



13. Very fine soft black argillaceous shales, with a few laminae of gray sand- 



stone. In the lower part of the group the shales are coal-black, but as 

 we ascend they become gray-black. Nearly all the layers are fossilifer- 

 ous. Among the forms are Prionocychis tvyomingensis, Sca/phiies [icarrcni~], 

 and Inoceramus \labiatus']. They are especially abundant near the top. .. 60.} 



14. Fine gray and yellowish shales 31 



15. About 17 feet of gravel, composed largely of basaltic bowlders, forming the 



top of the bluif. 



Total, about 687± 



These shales rest on sandstones referred to the Dakota. In this dis- 

 trict Dr. Peale estimates the total thickness of the shales belonging to 

 the Fort Benton , Niobrara, and Fort Pierre at 1,500 to 2,000 feet. 



A large part of Castle valley in eastern Utah is underlain by shales 

 like those above described, and at a horizon in them about 1,000 feet 

 below the Montana sandstones exposed to the Book Cliffs I have col- 

 lected Prionocyclus ivyomingcnsis, Scap kites icarreni, Baculites gracilis?, 

 and Inoceramus dimldius. 



Farther south in western New Mexico and in Arizona, the sections 

 described by Mr. G. K. Gilbert, 2 contain a greater proportion of sand- 

 stone, but the lower 850 feet, which is the only portion from which 

 fossils were obtained, evidently belongs to the Colorado formation, and 

 perhaps in the lowest layers to the Dakota. The highest fossiliferous 

 horizon noted is at Stinking spring, near Fort Wingate, New Mexico, 

 and it yielded Inoceramus labiatus and Ammonites. 



i Ann. Rept. U.S. Geol. Sur. Terr, for 1874, p. 136. 



2 U. S. Geog. and Geol. Sur. West «nc hundredth meridian, vol. in, pp. 514, 549-554. 



Bull. 10G 3 



