376 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. 



It is parted from the Onondaga- Salt group throughout most of Western 

 New York by a few inches of sandstone, as already stated. 



Position. — It is seen at Cherry Valley, &c, to dip south ; and it 

 is probable that the dip increases at no great distance from where 

 the rock disappears. This would readily account for higher rocks 

 in the series presenting themselves at the levels where we find them. 

 There are also undulations (Vanux. Rep. p. 134). 



Thickness. — This varies from ten to forty feet, and decreases west- 

 wards, the stratum being only fourteen inches thick at Black Rock 

 on the River Niagara. 



From its varying thickness, the materials of this limestone must 

 have been unequally distributed over the bed of the ocean, lodging 

 in depressions of the previous surface ; or these greater develop- 

 ments are only local and due to coral-reefs, but whether circular 

 or straight is not known. There was more than a single line of reef 

 (Vanuxem). 



Fossils. — These have not been properly arranged. They are nume- 

 rous, and mostly zoophytes. This rock presents 39 new or original 

 organisms, most of which are Brachiopoda and Zoophyta. It 

 receives 2 Zoophytes and transmits 1 Monomyarian mollusc (Avicula 

 pectiniformis, Hall, Conrad) ; 33 of its species perished, and are be- 

 come typical. Hall's researches will alter these figures. In the 

 Upper Helderberg group he expected, in 1854, to describe 100 spe- 

 cies, besides Bryozoa and Zoophytes. 



This rock is frequently made up entirely of broken corals and 

 crinoids, often tinted pink. It is, in fact, a mere coral-reef for large 

 spaces. An Ichthyodorulite has been found here, and a Lithoden- 

 dron. 



Fossils occurrent in Europe. — Encrinus Icevis is met with in Eng- 

 lish Wenlock, as well as Favosites alveolaris (Hall). 



Fossils recurrent in New York. — These are Catenipora escha- 

 roides, Favosites alveolaris, and F. gothlandica from the Upper 

 Silurian stage, together with Leptcena depressa, which enters the 

 Corniferous limestone. To these we have only to add the universal 

 Atrypa reticularis. 



Corniferous Limestone*. 



Mineral Character. — Especially at the east end of its range, this 

 is a fine-grained, compact limestone, light greyish-blue, dark-blue, 

 black, or even drab. It contains hornstone in nodules and layers, 

 sometimes to the exclusion of limestone, as is nearly the case at the 

 mouth of the River Niagara (north side), where the layers are black 

 and very rugged. In the higher parts of the rock there is sometimes 



* Professor Rogers calls the Upper Helderberg Limestone of New York (that is, 

 the Corniferous and Onondaga) the " Post-meridian Series." He recognizes it as a 

 widely-expanded marine limestone, and as the upper part of the Cliff Limestone 

 of the west. He observes, also, that it contains nodular chert, many fossils, 

 ganoid Devonian fish, Devonian and Carboniferous fossils — Productus and Pen- 

 tramites, — showing that even Carboniferous races tenanted the waters of the 

 Appalachian post-meridian sea (Johnston's Atlas, new edit. p. 31). 



