552 HISTORICAL GEOLOGY. 



Foerste reports the absence of several Clinton fossils from the Clinton beds along the 

 borders of the Cincinnati geanticline in Ohio and Indiana that occur in New York (£. S. 



According to Salter, a number of species of the Upper Silurian, and probably of this 

 part of it, have been observed in Arctic rocks on the shores of Wellington and Barrow 

 Straits and on King William's Island, lat. 72° to 76° ; Hali/sites catenulatus, Orthis 

 eleganttda, Favosites Gothlandiciis, Leperditia Baltica Hisinger, species of Calophyllum^ 

 Heliolites, Cijstiphyllum, Cyathophyllum, Syrincjopora, with Pentamerus conchiduim 

 Dalm., Atrypa reticularis, etc.; and, at the southern extremity of Hudson Bay, Penta- 

 merus oblongus, Atrypa reticularis, etc. Trochoceras boreale Foord is from Wellington 

 Channel. Between 79° and 82° 5', the expedition of Captain Nares obtained, accord- 

 ing to Etheridge, Corals of the genera Halysites, Favosites, Heliolites, Favistella, Zaph- 

 rentis, Amplexus, Cyathophyllum, and Arachnophyllum, and Trilobites of the genera 

 Bronteus, Calymene, Encrinurus, and Proetus, with Brachiopods of Pentamerus, Bhyn- 

 chonella, Chonetes, Atrypa, Strophomena. About Lake Winnipeg, also. Upper Silurian, 

 fossils have been found. See Am. Jour. 8c., 11., xxi. 313, xxvi. 119 ; III., xvi., 1878. 



The beds of northern Maine, about Square Lake, described by C. H. Hitchcock, have 

 afforded both Niagara and Lower Helderberg fossils, and many of them are made new 

 species by Billings. 



The Niagara beds of the vicinity of Cobscook and Penobscot bays, Maine, contain, 

 besides Niagara fossils, some of the Clinton group ; the latter, in Penobscot Bay, are 

 mostly confined to the lower half, but many Niagara species occur with them. (Shaler, 

 1886 ; Dodge and Beecher, 1892.) 



2. The Onondaga Period, 

 rocks — kinds and distribution. 



The Onondaga period embraces two somewhat unlike formations ; one^ 

 the Salina beds of shales and marlytes, or the Salt group, the source of the 

 brines of central New York and of rock salt in the Avestern half of the 

 state, as well as in Ontario and Ohio ; the other, the Water-lime group, in. 

 general an impure limestone, along with the overlying TentacuUte limestone. 

 Each was of shallow water origin, and partly marsh-made ; but the former was. 

 produced under conditions suited for the deposition and storing of salt from 

 the sea water. This classification was first proposed by D. Sharpe, in 1847. 



The following sections (Figs. 790, 791, from Hall), taken on a north-and- 

 south line south of Lake Ontario, show the relations of the Onondaga beds 

 {6,a, b) to those above and below, — they being underlaid in one section 

 (Fig. 790) by the Niagara beds (5 c), Clinton (5 b), and Medina (5 a), and 

 overlaid in the other (Fig. 791) by rocks of the Upper Helderberg (9), 

 Hamilton (10 a, 10 b, 10 c) and Portage group (11), the Lower Helderberg 

 being there absent. 



The rocks spread eastward to the Hudson River valley, the Water-lime 

 occurring as a thin stratum even east of the river. in the base of Becrafts- 

 Mountain, near Hudson, N.Y., and also in Mount Bob, a few miles farther 

 north, in each case resting on the upturned Hudson formation. They 

 increase in thickness westward. They extend beyond New York over much 

 of Ohio, cross Ontario to Lake Huron and northwestward to Mackinac in 



