8 Canadian Record of Science. 



of the Cretaceous needs to be invoked, other than those 

 mutations of land and water which the geological deposits 

 themselves indicate. A condition for example of the 

 Atlantic basin in which the high land of Greenland should 

 be reduced in elevation and at the same time the northern 

 inlets of the Atlantic closed against the invasion of Arctic 

 ice, would at once restore climatic conditions allowing of 

 the growth of a temperate flora in Greenland. As Dr. 

 Brown has shown, 1 and as I have elsewhere argued, the 

 absence of light in the Arctic winter is no disadvantage, 

 since, during the winter, the growth of deciduous trees is 

 in any case suspended ; while the constant continuance of 

 light in the summer is, on the contrary, a very great stimu- 

 lus and advantage. 



It is a remarkable phenomenon in the history of genera 

 of plants in the later Mesozoic and Tertiary, that the older 

 geiera appear at once in a great number of specific types, 

 which become reduced as well as limited in range down to 

 the modern. This is no doubt connected with the greater 

 differentiation of local conditions in the modern ; but it 

 indicates also a law of rapid multiplication of species in the 

 early life of genera. The distribution of the species of 

 Salisburia, Sequoia, Platanus, Sassafras, Liriodendron, Mag- 

 nolia, and many other genera, affords remarkable proofs of 

 this. 



Gray, Saporta, Heer, Newberry, Lesquereux, and Starkie 

 Gardner, have all ably discussed these points ; but the con- 

 tinual increase of our knowledge of the several floras, and 

 the removal of error as to the dates of their appearance 

 must greatly conduce to clearer and more definite ideas. 

 In particular, the prevailing opinion that the Miocene was 

 the period of the greatest extension of warmth and of a 

 temperate flora into the Arctic, must be abandoned in 

 favour of the later Cretaceous and Eocene ; and, if I mistake 

 not, this will be found to accord better with the evidence 

 of general geology and of animal fossils. 



While the Memoir, of which the above are the conclu- 



1 Florula Discoana. 



