THE CANADIAN JOURNAL. 



NEMT SERIES. 



No. LXXVI.— JULY, 1872. 



CONTEMPORANEITY OF STRATA 



AND THE 



DOCTRINE OF GEOLOGICAL CONTINUITY. 



BY H. ALLEYNE NICHOLSON, M.D., D.Sc, M.A., F.R.S.E., F.G.S., &c., 



Professor of Natural History and Botany in University College, Toronto. 



When groups of beds in different parts of the earth's surface, 

 however widely separated from one another, contain the same fossils, 

 or rather an assemblage of fossils in which many identical forms 

 occur, they are ordinarily said to be "contemporaneous." That is to 

 say, they are ordinarily supposed to belong to the same geological 

 period, and to have been formed at the same time in the history of 

 the earth. They would, therefore, be unhesitatingly regarded as 

 ''geological equivalents," and would be classed as Silurian, Devonian, 

 Carboniferous, and so on. It is to be remembered, however, that it 

 is not necessary to establish such a degree of equivalency between 

 widely separated groups of strata, that the fossils of each should be 

 to any great extent specifically identical. It is sufficient that, whilst 

 some few species are identical in both, the majority of the fossils 

 should be "representative forms," or, in other words, nearly alKed 

 species. It is the object, however, of the present paper to show that 

 groups of strata presenting the same fossils, if widely removed from 

 one another in point of distance, can only exceptionally be '■'■ contem- 



