The Position of the Cincinnati Group. 99 



" There are probably few well informed geologists who will, at the 

 present time, maintain that the occurrence of a very similar, or even 

 the same group of fossils, at widely separated localities, necessarily 

 proves the rocks in which they are found to be of exactly contempor- 

 aneous origin. The most that is now generally maintained in this re- 

 gard is, that such identity or correspondence of types, at very distant- 

 ly separated parts of the world, indicates that the strata in which 

 they are embedded were formed during the prevalence of identical 

 or similar physical conditions at some time during the same great 

 geological epoch, and that they hold the same, or nearly the 

 same, relative position in the geological column of their respective 

 districts. For instance, although a stratum in the Eocky Moun- 

 tains, containing the remains of very nearly the same fauna as some 

 particular subdivision of the Devonian system of Europe, might, for 

 aught we know, be hundreds of years older or newer than that par- 

 ticular division, we Avould have little or no room for doubting that 

 it belonged to the great Devonian series, or possibly even to some 

 definite known horizon in that series. We could, moreover, very posi- 

 tively assert, in such a case, that it would be, according to all past ex- 

 perience, useless to seek there at any lower geological horizon for 

 workable beds of coal, or to expect to find Silurian rocks, or any of 

 their peculiar products, above, supposing there had been no overturn- 

 ing of the strata at the particular localities. 



" Hence, although paleontology does not enable us to ascertain the 

 exact actual ages of rocks, when applied with due caution and skill in 

 connection with a careful observance of their stratigraphical arrange- 

 ment, and lithological and other physical characters, it does afford the 

 means of fixing their relative ages, as well as of identifying the same 

 beds at different localities, within given fields of observation, with 

 very considerable precision. It is, therefore, not merely one of the 

 more important aids to the geologist in his investigations, but in the 

 present state of geological science, it is the only sure guide in classify- 

 ing and determining the order of succession of rocks, where this can 

 not be done by their actual continuity or obvious superposition." 



The Laurentiau series of metamorphic rocks forms the base of the 

 sedimentary strata, and has an estimated thickness of 32,750 feet. 

 (Geo. of Can., 1863, p. 45.) It takes its name from the Lauren- 

 tian Mountains of Canada. Eozoon Canadense and other fossil fora- 

 minifera have been found at the base of the Grenville band of lime- 

 stone, which is placed about the middle of this great series. The 

 estimated depth of the Laurentian series to the lowest place at which 

 the Eozoon Canadense has been found, is 16,500 feet. Sir W. E. Lo- 



