BY R. M. JOHNSTON, F.L.S. 137 



persistent terrestrial forms of life to the antipodes of their 

 origin would probably in most cases occupy a vast period 

 of time ; and consequently the typical forms of a given 

 horizon in one hemisphere should rather be sought in a 

 succeeding horizon in the opposite hemisphere, and vice 

 versa ; and the equivalents of a given subdivision in one 

 geographical province are more likely to be indicated by 

 the local breaks of far distant regions rather than by any 

 local division represented, with which alliances are too 

 frequently sought on the strength of the association of 

 two or three typical genera which they may happen to 

 possess in common. 



The danger of this common tendency has already been 

 fully discussed under classification and nomenclature of 

 the Mesozoic period.'' The great difficulty of correlating 

 widely separated provinces, by reference to the association 

 of typical organisms of any one distant region, is in no 

 way concerned with absolute contemporaneity/, for that 

 might be reconciled by the theory of homo taxis, as defined 

 by Professor Huxley. 



The conception of the commingling of types from widely 

 separated independent centres of origin — a most probable 

 one — frustrates any attempt by the usual references to fix 

 the sequence and exact relationship of ^the rocks of widely 

 separated countries. 



Towards the close of the Mesozoic period, and during 

 the Tertiary period, physical, climatic, and organic changes 

 of a remarkable character took place, both in the northern 

 and southern hemispheres. Dr. Geikie states that some 

 of the most colossal disturbances of the terrestrial crust of 

 which any record remains took place within the Tertiary 

 period ; and adds : " Not only was the floor of the 

 cretaceous sea upraised into lowlands, with lagoons, 

 estuaries, and lakes, but throughout the heart of the Old 

 World, from the Pyrenees to Japan, the bed of the early 

 Tertiary or nummulitic sea was upheaved into a succes- 

 sion of giant mountains, some portions of that sea floor 

 now standing at a height of at least 16,500 feet above the 

 sea." In the southern hemisphere there is no evidence of 

 Tertiary marine beds having been found at a greater 

 altitude than 2000 feet above the existing sea level, but 

 the almost continuous mass of marine formations in Aus- 

 tralasia, from Cape York to Tasmania, testify of the won- 



» Proc. Roy. Soc, of Tas., 1886, (pp. 164-169 ;;^181-182). 



