STEATIGEAPHICAL GEOLOGY. 13 



The Upper Helderberg Group, in its fullest development, consists of four 

 members, the Caudagalll grit, the Schoharie grit, the Onondaga and Corniferous 

 limestones. The first, when characteristic, is a dark, gritty slate, which has a cleav- 

 age vertical to the line of deposition, and is generally destitute of fossils ; but with 

 surfaces, covered with curved, fucoid-like markings, which have given it its 

 name. This rock constitutes beds of passage from the Oriskany sandstone, and 

 graduates above into the Schoharie grit, which is an arenaceous limestone, 

 weathering to a brownish color, and succeeded by the gray, subcrystalline, coral- 

 line formation, which is known in New York as the Onondaga limestone, while 

 the Corniferous limestone consists of the higher dark-colored chert beds of the 

 Group. (Hall's Pal., vol. iii., p. 43.) 



The Caudagalli grit was named from a fucoid having some resemblance in 

 form to the tail of a chicken cock. It has a small geographical range, and its 

 maximum thickness in New York is placed at 70 feet. 



The Schoharie grit, named from Schoharie, New York, has a small geo- 

 graphical range and no considerable thickness. In Pennsylvania and New 

 Jersey, where the Caudagalli and Schoharie grits have been called the Post Meri- 

 dian grits, they have a, thickness of 300 feet. This Group in New York consists 

 of a fine grained calcareous sandstone, somewhat resembling the Oriskany, but 

 bearing quite different fossils. 



No vertebrate animal has yet made its appearance. 



The Onondaga limestone is only from 20 to 50 feet thick in New York, and, 

 though traced over a great extent of country, rarely exceeds that thickness. In 

 Missouri it is said to vary from 10 inches to 75 feet in thickness, but there are 

 few if any Western localities where this Group can be separated from the Cor- 

 niferous. 



The Corniferous limestone was named from the chert, found in it, which 

 breaks with a corny fracture. It varies from 100 to 200 feet in thickness, in 

 Ohio, Indiana, Illinois, Pennsylvania and New York. It is from 300 to 400 feet 

 thick in Michigan, and reaches its maximum of 850 feet at Tilsonbury, Canada. 

 At Louisville, Kentucky, this Group consists of a mass of fossil corals, in a bed 

 of hard limestone. It has the appearance of having been a coral reef, and has 

 been so designated, but the limestone is so firm that perfect specimens of the 

 corals are not easily procured. 



This is the Group of rocks in which the first remains of vertebrate animals 

 are found. These remains consist generally of the teeth of fish, but other hard 

 parts are also found. Some styata are known which are literally a mass of fish 

 teeth cemented together in a compact limestone. Land plants become more com- 

 mon in this Group. 



The maximum of these subdivisions of the Upper Helderberg Group is there- 

 fore 1,225 feet. Each subdivision in New York is characterized by distinct fos- 

 sils, but in Canada several of the most characteristic species of the Oriskany 

 sandstone ascend through each of the overlying Groups into the Corniferous. 



From this time forward, the five sub-kingdoms in animal life are represented 

 in every Group of rocks capable of their preservation, viz. : Protista, Radiates, 

 MoUusks, Articulates, and Vertebrates. They all continue to change and de- 

 velop, but the great field of evolution is well nigh surrendered to the Vertebrates, 



