86 THE MOUNTAIN. 



In some places it has attained the thickness of 600 feet, 

 but in other places it is not more than 50 feet thick. 



FORMATION 8 



Is a large mass of rocks, called the " olive slate group, or 

 the Hamilton, Portage, and Chemung groups" of the New 

 York reports. It is composed of a series of dark-gray and 

 olive slates and sandstones, sometimes yellow, greenish, and 

 brown. The sandstones are argillaceous and fine-grained, 

 showing extensive and peculiar lines of cleavage. 



At the base of the mass it abounds in fossils ; but fossils 

 are found through the whole formation, some localities 

 giving several species of trilobites. There are also in it 

 . shells and corals in abundance. It is from 5000 to 8000 feet 

 thick, and, wherever distributed, presents a characteristic 

 style of topography, with great sameness of soil, quality of 

 surface, etc. etc. 



FORMATION 9 



Reposes upon the last group described, and is a large 

 mass of rocks composed of red slates and shales, red, gray, 

 and brown argillaceous sandstones and slates. This is the 

 group which forms the southeastern slopes of the Alleghany 

 Mountain, and is extensively exposed in all the gaps or 

 cuts of the mountain. 



It also forms the slopes of the mountains in the anthra- 

 cite regions. Some of the northern counties have a con- 

 siderable portion of their surfaces formed of this and asso- 

 ciated masses, as Pike, Wayne, and Monroe counties. It 

 contains fossil shells, and beautiful vegetable fucoidal forms 

 in abundance, as cock's-comb fucus, etc. 



It is frequently 6000 feet thick, and sometimes more ; and 

 is the Catskill group of the New York reports. The whole 

 is a mass of sand and mud rocks, a bright-red being the 

 predominating color. It also contains an iron ore of 

 value, and some copper. 



