98 TJie Position of tJie Cincinnati Group. 



The geological column is therefore to be regarded as one continuous 

 whole, commencing at the base of the metamorphic rocks, and con- 

 tinuing without interruption, and without any break in animal life up 

 through the sedimentary deposits of the present time. The division 

 into systems or formations is retained for convenience to embrace a 

 collection of consecutive groups having some character in common, but 

 not to be understood as necessarily embracing every group having such 

 common characteristic, nor as denying that any group in one system 

 or formation may not have the same lithological appearance, or possess 

 some of the same fossils that a group in another system or formation 

 may have or possess. The division into groups is likewise one of con- 

 venience, though it is much more expressive, and less liable to be misun- 

 derstood in its actual significance than the older division into systems 

 or formations. By a group we understand, a series of rocks either hav- 

 ing the same general lithological appearance, or, though quite difterent 

 in appearance, having the same fossil contents in general, or sometimes 

 merely signifying the exposure of the strata at a particular locality. 



In general it is only through a knowledge of paleontology that 

 strata or groups of rocks at distant places can be compared, and their 

 order of superposition determined. Such knowledge is the key which 

 unlocks and opens to view many miles in thickness of the surface of 

 the earth, and carries us back on a train of thought and observation 

 through many millions of years in time, and through the history of 

 animal development from the highest vertebrate animals of to-day to 

 the foraminifera of the Laurentian Group. 



The strata of rocks constituting the Cincinnati Group, though situ- 

 ated at a station on this road far below the fossil remains of the verte- 

 brate kingdom, are yet in the upper half of the geological column of 

 fossiliferous rocks not only of North America, but of their equivalent 

 in Europe and throughout the world. 



The immense exposures of the Laurentian, Huronian and Quebec 

 rocks, in separate sections in Canada, the Potsdam in Tennessee, the 

 Catskill in Pennsylvania, and the Coal Measures in Nova Scotia, have 

 afforded the opportunities for measuring the groups having the great- 

 est thickness without appealing to the fossil contents for any assistance; 

 nevertheless the determination of their order of superposition with re- 

 gard to each other has somewhat depended upon their fossil contents, 

 and that of adjacent underlying or superimposed strata, while many of 

 the smaller groups have been placed in the geological column, after a 

 careful examination and thorough knowledge of their fossil contents, 

 which alone has enabled us to determine their relative position. 



Prof. Meek, in the introductory remarks to his report on the paleon- 

 tology of Eastern Nebraska, says : 



