NORTH AMERICAN GEOLOGY. 203 



resented by a very liuiiteu area yiekliny; plant remains. The Silurian 

 consists in greater part of slate, with thick beds of limestone, approxi- 

 mately Lower Helderberg in age. The members of the Cambrian-Silu- 

 rian series are mostly slates and sandstones greatly disturbed, and in 

 some places graduating into beds of micaceous schists.* 



42. Messrs. Seely and Brainard describe the geology in the vicinity of 

 Fort Cassin, Vermont, near the shore of Lake Champlain. The district 

 is one of simple monoclinal structure, with gentle dips. The strata are 

 Lower Silurian limestone, some beds of which yielded a fauua of many 

 new species, which are described and figured by Whitfield, who also dis- 

 cusses the horizon of the beds.t 



43. Dartou, in a paper on the Upper Silurian at Cornwall Station, Oran ge 

 County, New York, describes an outlier of Lower Helderberg limestone 

 lying npon beds of conglomerates and shales, forming an outlier far dis- 

 tant from the main mass of the formation. The Water- Lime, Pentame- 

 rous and Delthyris Shaly are recognized by abundant fauna. The beds 

 are uptilted at a high angle, and the greatest exposed thickness is about 

 100 feet, the outcrop having a length of about half a mile along a ISTXE. 

 and SS W. strike. | The same writer announces the approximate Niagara 

 age of the fossiliferous limestone associated with the Green Pond Mount- 

 ain series at Upper Longwood, and in Newfoundland, New Jersey, which 

 had been considered Trenton by Cook. § 



44. S.G.Williams gives an accountof additional observations upon the 

 westward extension of rocks of Lower Helderberg age in New York. 

 He finds the group, including all above the Water- Lime, to be represented 

 at least as far west as Cayuga Lake by limestones not less than 65 feet 

 in thickness, and carrying an unmistakable fauna. The gypsiferous 

 limestone of Cayuga County holds a mixed Tentaculite and Lower 

 Pentamerous fauna. At the outlet of Skaneateles Lake and at the Oris- 

 kany Falls, near Utica, the formation is represented by the Tentaculite 

 limestones, which at the last-named place is overlain by mixed Lower 

 Pentamerous and Delthyris Shaly. From the increasing indistinctness 

 of the divisions, and the predominance of the lower portion of the 

 Lower Helderberg to the westward and of the Salina Group to the 

 eastward, it is concluded that the two groups may have been deposited 

 simultaneously, or at least so in part. || The same author, in a paper on 

 the Tully limestone of New York, calls attention to its outcrop line and 

 flexures, and gives an account of its fauna, which includes 120 species.^ 



45. Pohlman describes a well-hole near Buffalo, New York, in which 

 1,305 feet of Onondaga strata were pierced, the well ending in soft 



* Canada Geol. Survey, Report for 1885. 



t Aiuerican Mus. Nat. Hist. Bulletin, vol. 1, pp. 293-348, and pis. 



t Am. Jour. Sci., in, vol. 31, pp. 209-216. 



§ Hunt's Mineral Physiology and Pliysiography, p. 591. 



II Am. Jour. Sci., iii, vol. 31, pp. 139-145. 



If Am. Assoc. Proc.j vol. 35, pp. 213, 214. 



