CONTEMPORANEITY AND PIOMOTAXIS. 47 



science, as also in Palaeontology itself, but they led at first to erron- 

 eous generalisations. When it had been clearly established that 

 particular groups of strata in Europe were characterised by particular 

 assemblages of animals and plants, it was, not unnaturally, concluded 

 that similar or identical assemblages of organisms would be found to 

 characterise corresponding groups of strata all over the world. This 

 led to the idea that the successive faunae and florae observable in the 

 area first examined had been universally distributed over the tvhole 

 globe ; from which followed the old catastrophistic view that the 

 close of each geological period had been signalised by a more or less 

 complete extinction of the animals and plants then in existence, and 

 that a new fauna and flora had been introduced at the commence- 

 ment of each succeeding period. 



It is, however, now universally admitted that in nature the chron- 

 ological succession of the rocks, as determined by fossil remains, is 

 local and not universal — in the sense that the precise order of phen- 

 omena must necessarily have differed in different regions. That this 

 must be so is proved by the existence at the present day of " zoolog- 

 ical provinces " ; by the fact that dry land and sea must always have 

 existed since the beginning of Palaeozoic time at any rate, and that 

 sedimentation can, therefore, never have been universal ; and by the 

 certainty that the sedimentary deposits now in process of formation, 

 and therefore necessarily coeval, contain the remains of dissimilar 

 groups of animals and plants. 



In view of these considerations, it is necessary to consider what 

 precise significance is to be attached to the term " contemporaneous " 

 as applied to different groups of strata. 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 or closely allied species occur, they 

 are generally 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 ordinarily regarded as " geological equiva- 

 lents," and would be classed as Silurian, Devonian, Carboniferous, 

 and so on. The use of the term " contemporaneous " in the above 

 comprehensive sense cannot, however, be accepted without serious 

 qualification. Within the limits of a single geographical area of 

 moderate size, beds containing identical, or nearly identical, fossils, 

 may doubtless be safely regarded as strictly " contemporaneous," since 

 there is no reason why such should not have been deposited within 

 one ocean, and during a single geological period. When, on the 

 other hand, we find precisely identical or even representative species 

 of fossils in beds which are very widely removed from one another 

 geographically, there is a presumption that such beds are not exactly 



