368 THE JOURNAL OF GEOLOGY. 



As long ago as 1853 Pictet, in his then celebrated Traite de 

 Paleofitologie, presented a number of general principles, among 

 them being one, the so-called eighth law, which bears directly 

 upon the present question. It is as follows : "Contemporaneous 

 deposits, or those formed at the same epoch, contain identical 

 fossils. Conversely : deposits which contain identical fossils are 

 contemporaneous." This was modified by Schimper,^ the cele- 

 brated French paleobotanist, who added that deposits "formed 

 at the same epoch, contain floras, if not completely identical, at 

 least homologous, and consequently deposits that contain iden- 

 tical or homologous floras are contemporaneous." But Huxley 

 appears to have been the first (1862) to formulate clearly the 

 objections to this law. He pointed out that while the succes- 

 sion of life in widely separated localities may be shown to have 

 been similar, it by no means follows that the identical elements 

 in these widely separated localities were strictly contemporane- 

 ous. To this he applied the term honotaxis, which implies that 

 the plants and animals of widely separated places may have 

 had practically the same process of development or succession, 

 yet when the element of time is considered they may have been 

 far from identical. As an example it may be mentioned that 

 the most abundant and typical genus of plants in the Carbonifer- 

 ous rocks of Australia and Tasmania is Glossopteris, a genus 

 which is not represented in rocks of similar age in Europe, but 

 occurs in Upper Mesozoic beds of that region. 



This, it will be readily understood, applies to localities widely 

 separated, as for example between continents that are not inti- 

 mately connected, or that are now and have been for a long 

 geological period separated by insurmountable barriers to immi- 

 gration, such as oceans and mountain chains. The plants origin- 

 ating within a given area or the ones inhabiting a locality adapt 

 themselves to the environment, and these can only extend their 

 distribution readily to areas in which the conditions are similar. 

 Hence if the particular locality in which a species has been 

 developed is separated from other areas, perhaps as well suited 

 ^ Traits de Pal. Vdg., Vol. L, 1869, p. 100. 



