AGE OF THE ORISKANY SANDSTONE. 191 



been at work during any period are well understood, and where the 

 flora and faunae are clearly defined, it is generally easy to determine 

 the horizon which separates the group of rocks to which they belong 

 from others either above or below. But there are cases in which 

 this line of separation is very obscure, so that whether a formation 

 belongs to this or that group becomes a question not so easily de- 

 cided. Such you are aware is the case with respect to the Trenton 

 Limestone in Canada, which, in the United States, the New York 

 Geologists divide into three formations, each characterised with good 

 natural horizons of separation. This is the question at issue re- 

 specting a primordial zone in America ; and the same difficulty is 

 experienced in fixing the age of the Oriskany Sandstone formation. 



This formation, though of little thickness, has a very wide range 

 — extending from the Peninsula of Gaspe to Lake Huron. It is 

 generally regarded as belonging to the Devonian, and forming the 

 base of that system, while some authors think that it should be 

 classed with the Upper Silurian, These gentlemen base their con- 

 clusion upon pseleontological evidence. It is not my intention to 

 discuss that evidence, but simply to furnish a few facts which appear 

 to bear upon the subject, and lead to an inference quite contrary to 

 that come to by those who class it with the Silurian. 



Beneath the Oriskany Sandstone in Western Canada occurs a 

 group of rocks, known as the Onondaga Salt or Q-ypsiferous group. 

 The following ascending section of a few of the upper beds will be 

 sufficient to explain their character : — 



ft. in. 



Brownish grey shaly limestone 5 



Water lime containing Euryptersus (?) 2 6 



Hard grey shaly limestone weathering brown 1 



Hard porous brownish drab crystalline limestone, in 



beds of from 1 to 3 feet in thickness 5 



Thick-seamed conglomerate limestone composed of a 

 light grey paste, holding small angular masses of a 

 more compact, hard, dark grey coloured lime with a 

 brownish tint, the whole yellowish on weathered sur- 

 face 4 



Porous grey limestone, containing numerous irregular 

 bluish bands, lighter coloured on weathered surface. 



