233 GEOLOGICAL DISTRIBUTION. 



mammalian beds of Pikermi, Greece, with Hipparion, Dinotherimn 

 giganteum, &c., which are generally classed by geologists as Mio- 

 cene, or Mio-Pliocene, actually overlie marine deposits of almost 

 unquestionably Pliocene age. In the Gondwana system of rocks of 

 the peninsula of India the Damuda group, whose fiora is stated to 

 be more nearly allied to the Jurassic flora of Europe than to any 

 other, is overlaid by deposits holding an apparently Rhaetic flora, 

 and these, again, are succeeded by beds whose faunal characters 

 partake of the Tiiassic period. The coal-bearing beds of Southern 

 and Eastern Australia are claimed by paleobotanists to be typically 

 Jurassic, while the interstratified marine beds, in the character of 

 their animal remains, are just as unequivocally Carboniferous. In 

 the Laramie formation of the Western Territories of the United 

 States we have a somewhat similar association of an Eocene Tertiary 

 flora, many of whose species are identical with forms occurring in 

 the Island of Sheppey, and elsewhere in Britain, with a vertebrate 

 fauna of a distinctively Cretaceous type. 



That there should be no direct correspondence existing between 

 the chronological facies of the marine and terrestrial faunas and 

 floras is not very surprising, seeing that there exists no reason why 

 their special development should have covered equal periods of 

 time. Nor could it be i-ationally expected, in view of the variable 

 physical conditions prevailing over the land-surface, and the inter- 

 position of impassable water-barriers, that the development of a 

 land fauna or flora should, in itself, be equal for all parts of tlie 

 earth's surface, even though these parts enjoy approximately the 

 same climatic influences. This negative condition is beautifully 

 exemplified in the utter dissimilarity of the modern mammalian 

 faunas of South America, Africa, and Australia, which, had we 

 known them in a fossil state, might have been taken to indicate 

 three very distinct periods of geological time, and the same might 

 have been said, in great measure, of their floras. Yet, were the 

 marine faunas belonging to these different regions examined, there 

 could be but little doubt as to their representing chronological 

 equivalents. It is, therefore, not very remarkable, and not specially 

 indicative of the existence of climatic zones, that the Australian 

 coal-flora should be of the type which is elsewhere represented in 

 the Jurassic deposits, and that it should be associated with a dis- 

 tinctively Carboniferous marine fauna. And no more remarkable is 



