Mesozoic and Coinozoic Geology and Palmontology. 155 



Orange, Chatham, Moore, Montgomery, Richmond and Anson counties, 

 and extends about six miles into South Carolina. Its length is about 

 120 miles, and it has a breadth, in the widest part, of 18 miles, though 

 its width is generally about six miles. 



In 1859, Major Hawn* gave a section in Kansas, of rocks 410 feet in 

 thickness, which he referred to the Triassic. But Dr. Mudge has 

 maintained since that time, that the cretaceous rocks rest directly upon 

 the Permian, in that State. 



In 1860, Meek & Haj^denf described, from the Jurassic, at the south- 

 west base of the Black Hills, Pholadomya humilis, 3Iyacites nebras- 

 censis, Thracia araiata, T. sublcevis, Cardium ahumardi, Tancredia 

 fp.quilateralis, T. xvarrenana^ Astarte fragilis, A. inornatn, Trigonia 

 conradL Pecten extenuatus^ now C amjjtonectes extenuatus, and from 

 Red Buttes, on the North Platte, Ostrea engelmanni, Pecten hellis- 

 friata, now Camptonectes bellistriatus, and Dentalium s ubquadratum. 



And Wm. M. Gabb;]; described, from the Triassic in Bath county, 

 Virginia, Ceratites virgin ianus and Phynchonella halli. 



In 1861, Dr. F. V. Ha3'den,§ in his reconnoissance of the countr}?^ 

 about the headwaters of the Missouri and Yellowstone rivers, found 

 the red arenaceous deposits, usually referred to the Triassic age, 

 exposed in outcropping belts, from one to two miles wide, around the 

 margins of the mountain elevations, but not generally otherwise ex- 

 posed. They occur on the northeastern side of the Big Horn moun- 

 tains, on the west slope of the Wind River mountains, along the moun- 

 tains al the source of the Missouri, around the Judith mountains, 

 and at numerous other places. Frequently thick layers of gypsum 

 are found in the deposits. The thickness observed is from 1000 to 

 1500 feet. 



He also found the Jurassic rocks overlying the red arenaceous beds, 

 referred to the Triassic, and possessing an equal geographical exten- 

 sion. They are found along the margins of the Black Hills, along 

 the northeastern slope of the Big Horn mountains; at Red Buttes; 

 along the southwest side of the Big Horn, and the northeast side of 

 the Wind River mountains, sometimes having a thickness of 1000 

 feet, and containing organic remains in the greatest abundance. 



In the same 3'ear, Meek & Hay den || described, from the Jurassic, at 



■■' Proc. Am. Ass. Ad. Sci. 



t Proc. Acad. Nat. Sci. 



X Jour. Acad. Nat. Sci.. 2d Ser., vol. iv. 



? Am. Jour. Sci. and Arts, 2d Ser., vol. xxxi, 



II Proc. Acad. Nat. Sci. 



