UPPER HELDERBERG GROUP. 59 



CHAPTER XX. 



UPPER HELDERBERG GROUP. 



§ 122. This Group was named from the Helderberg Mountains, where it was 

 divided into the Cauda-galli grit, Schoharie grit, Onondaga limestone, and Cornif- 

 erous limestone. The Corniferous limestone being the only one which has any 

 great geographical distribution, the Canadian Geologists in 1863 used " Cornif- 

 erous formation " instead of Upper Helderberg ; but as Corniferous is a mineral- 

 ogical word, Upper Helderberg is to be preferred. The Cauda-galli grit is a dark 

 gritty slate covered with Taomim* cauda-galli, and graduates into the Schoharie 

 grit, which is an arenaceous limestone weathering to a brownish color. These occur 

 in the eastern counties of New York, Albany, Greene, and Schoharie, but soon 

 thin out and are not found west as far as the center of the State. The scales and 

 bony plates of fish are first found in the Schoharie grit. The Onondaga is a gray 

 subcrystalline, coralline limestone. It is followed by the Corniferous limestone, 

 which bears dark-colored, cherty beds, that break with a horny fracture, which 

 suggested the name Corniferous; but the cherty beds occur in various places in 

 these two divisions, and there is no real line of separation between them. The 

 chert, or hornstone, is largely composed of microscopic, silicious forms of plants 

 or protophytes, spiculse of sponges, fragments of the dental apparatus of Gastero- 

 pods, and other organisms. The aggregate thickness of the Group in New York 

 is about 300 feet. 



§ 123. From New York the Group extends in a belt west across the penin- 

 sula of Canada to Mackinac Island, where it is 250 feet thick, and from thence 

 into Michigan where its thickness is 354 feet. It appears at Sandusky and North- 

 western Ohio, at Columbus, and on the Ohio a few miles below the mouth of 

 the Scioto, resting upon the Waterlime Group, which has great thickness in this 

 State. It crosses into Northern Indiana, and striking south-westerly, crosses the 

 Ohio River at Louisville. It appears in Illinois, Iowa, Missouri, and Tennessee, 

 resting on the Oriskany, or the Waterlime, or the Niagara, and everywhere pre- 

 serving the character of the great coral-reef period of the Devonian, but never 

 exceeding a thickness of about 300 feet. In New Jersey, however, the Cauda- 

 galli grit has a thickness of 400 feet, and the Corniferous limestone 500 feet, mak- 

 ing a total thickness of 900 feet. It occurs in the western mountain ranges, and 

 is one of the most persistent aud generally distributed Groups. 



§ 124. It is a marine limestone, distinguished for the remarkable abundance of 

 corals, and coral reefs, the variety in form, number, and size of species, some 

 specimens being several feet in diameter, and larger than any belonging to any 

 earlier period. It is distinguished also for its fish remains, which consist of teeth, 

 or the outer bony covering, sometimes so abundant as to constitute the major part 

 of layers, 3 or 4 inches, or even more, in thickness. Some were very large 

 and singularly constructed. The Macropetalichthys sullivanti had a head 15 inches 

 in length composed of hard, bony plates, covered with a thick skin dotted with 

 tubercles. Cephalopods are abundant and quite characteristic, and in a few places 

 drifted land-plants have been found, but they are not of general occurrence. The 



