Hypothetical Continents. 93 



Europe underwent during the tertiary period, there must also 

 be great changes taking place in its fauna and flora. Conse- 

 quently we find that the eocene flora of Europe is largely 

 Australian in its character,* that the miocene flora is largely 

 American and Japanese, and that the miocene shells are largely 

 East Indian. t Respecting this last character, I have shown 

 that the only legitimate inference to be drawn from it, is that 

 the mollusca emigrated from Europe in a south-easterly direc- 

 tion ; and this conclusion is borne out by the fact, that some 

 still exist in the Mediterranean and Red Seas, having been left 

 behind by the less hardy species, for the emigration was no 

 doubt chiefly the result of the climate having become colder, 

 in consequence of physical changes. This cooling of the 

 climate of Europe began towards the close of the eocene period, 

 for while the eocene fauna and flora were purely tropical, the 

 miocene were scarcely more than subtropical, and the pliocene 

 hardly more than temperate in some regions and much colder 

 in others. 



It is worth remarking, that the emigration of animals and 

 plants from Europe seems to have taken place more constantly 

 towards the east than in an opposite direction ; witness, for 

 instance, the affinity of the Australian mammals to those of our 

 oolitic rocks, the affinity of the eocene European plants to the 

 Australian recent, and the likeness of the European miocene 

 flora to the recent American and Japanese. The tertiary cha- 

 racter of the American cretaceous plants is notorious, as is 

 the miocene (European) and recent (American) character of the 

 eocene flora of that continent; I believe, therefore, that our 

 miocene plants came from America during the eocene period, 

 and that their progenitors were the plants of the eocene and 

 cretaceous periods in America, from which have also descended 

 the recent flora of that continent. 



If these views be admitted, the large number of Swiss 

 miocene species represented in America is naturally explained, 

 for the American plants had a double chance of preserving 

 their likeness to their descendants. Again, if the present flora 

 of America (or that from which it has descended), has existed 

 on that continent ever since the cretaceous period, we ought to 

 find the remains of it imbedded in leaf-bearing strata of all 

 succeeding periods in America, if such deposits exist. At 

 present, this crucial test is not available for periods later than 

 the eocene ; but the evidence at our command bears out, as we 

 have seen, the views I am advocating. 



* Ettingsliausen — Ueberdie Untdeclciaig des NeuJwlldndischen CharaJcters der 

 JEocenjlora JEuropds, 1862. Unger — New Holland in JSuropa, and Journal of 

 Botany, No. 26. 



f See Quarterly Journal of the Geological Society, vol. xx. p. 63. 



