
Boox V.] CONTEMPORANEITY AND HOMOTAXIS. 617 
Each formation being distinguished by its own assemblage of 
organic remains, it can be followed and recognized even amid the 
crumplings and dislocations of a disturbed region. The same 
general succession of organic types has been observed over a large 
part of the world, though, of course, with important modifications in 
different countries. This similarity of succession has been termed 
homotaais—a term which expresses the fact that the order in which 
the leading types of organized existence have appeared upon the 
earth has been similar even in widely separated regions. 
It is evident that in this way a method of comparison is furnished 
whereby the stratified formations of different parts of the earth’s 
erust can be brought into relation with each other. We find, for 
example, that a certain series of strata is characterized in Britain by 
certain: genera and species of corals, brachiopods, lamellibranchs, 
_ gasteropods, and cephalopods. A group of rocks in Bohemia, 
differing more or less from these in lithological aspect, contains on 
the whole the same genera, and some even of the same species. In 
Scandinavia a set of beds may be seen unlike, perhaps, in external 
characters to the British type, but yielding many of the same fosssils, 
In Canada and parts of the northern United States, other rocks 
enclose some of the same, and of closely allied genera and species. 
All these groups of strata, having the same general facies of organic 
remains, are classed together as homotazial that is, as having been 
deposited during the same relative period in the general progress of 
life in each region. 
It was at one time believed, and the belief is still far from extinct, 
that groups of strata characterized by this community or resemblance 
of organic remains were chronologically contemporaneous. But such 
an inference rests upon most insecure grounds. We may not be 
able to disprove the assertion that the strata were strictly coeval, 
_ but we have only to reflect on the present conditions of zoological 
and botanical distribution, and of modern sedimentation, to be 
assured that the assertion of contemporaneity is a mere assumption. 
Consider for a moment what would happen were the present surface 
of any portion of central or southern Europe to be submerged 
beneath the sea, covered by marine deposits, and then re-elevated 
into land. ‘The river-terraces and lacustrine marls formed before 
the time of Julius Cesar could not be distinguished by any fossil 
tests from those laid down in the days of Victoria, unless, indeed, 
traces of human implements were obtainable whereby the progress 
of civilization during 2000 years might be indicated. So far as 
regards the shells, bones, and plants preserved in the various forma- 
tions, it would be absolutely impossible to discriminate their relative 
dates; they would be classed as “ geologically contemporaneous,” that 
is, as having been formed during the same period in the history of 
life in the European area; yet there might be a difference of 2000 
years or more between many of them. Strict contemporaneity 
* Huxley, Q. J. Geol. Soc, xviii. 1862, p. xlvi, 
