320 PROCEEDINGS OF THE ACADEMY OF [1887. 



to the geologist the data of an inftillible chronology. The absolute 

 succession of equivalent faunas, or faunas of a practically iden- 

 tical facies, which has been demonstrated for the greater jmrt of 

 the world, clearly establishes the claims of the faunal element as the 

 guide propre in the determination of chronology. It not only serves 

 to fix the relative sequence of formations for any one country, but 

 determines absolutely the position in time Avhich these formations 

 occupy in a geological scale constructed for the entire world. 



It is, however, contended, and apparently with force, that certain 

 physical phenomena associated with the disposition of rock-masses 

 are as clearly consecutive in their occurrence as is the progression of 

 the life series, and might, hence, claim equal importance as chrono- 

 logical determinants of the geological scale. Thus, it is pointed out, 

 we have the world over a i:)hysical break of definite importance be- 

 tween the Paleozoic and Mesozoic series of rocks, and a somewhat 

 similar break wanting in some parts between the Mesozoic and 

 Kainozoic ; and, again, minor breaks between the lesser formations. 

 But how could the equivalence of these breaks be determined were 

 it not for the predetermination of age through the faunal remains ? It 

 might be assumed, where a deposit of a definite or special litholog- 

 ical character can be continuously followed, such as coal or the chalk 

 of the Cretaceous period, that we are furnished with certain distinct- 

 ive data which here preclude the possibility of mistaking the act- 

 ual equivalence ; that, for exam})le, where we recognize the break 

 following the chalk in England we recognize a similar break in 

 France and Belgium, and likewise the same for the coal. But 

 by what method, other than the paleontological one, could the post- 

 Cretaceous break be identified or correlated in regions, such as the 

 Eastern United States, where the true chalk is wanting, and where 

 the beds representing it could, from lithological character, about as 

 well be taken to represent an older member of the series to which 

 they belong as a newer one? 



The notion held by some geologists that the true determinants of 

 a formation or, more properly speaking, the true measure of geo- 

 logical time, is found rather in the lithological than in the paleonto- 

 logical record, can not for a moment stand the test of a logical in- 

 quiry. To submit, for example, that the matter of continuous sed- 

 imentation, or the absence or presence of conformability, or the ex- 

 istence or non-existence of a physical (lithological) break, can in 

 any way affect a time-record based upon the uninterrupted succession 



