22 SIE J. W. DAWSON ON THE MESOZOIC FLORAS, ETC. 



selves indicate. A coucTitioii for example of the Atlantic basin in which the high land of 

 G-reeuland shoïild 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/ 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 stimulus and 

 advantage. 



It is a remarkable phenomenon in the history of geuera of plants in the later Mesozoic 

 and Tertiary, that the older genera appear at once in a great number of specific tyjîes, 

 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 indi- 

 cates also a law of rapid multiplication of species in the early life of genera. The distribu- 

 tion of the species of Salisbiina, Sequoia, Platamis, Sassafras, Liriodendron, Magnolia, and many 

 other genera, affords remarkable proofs of this. 



G-ray, Saporta, Heer, Newberry, Lesquereux and Starkie Gardner, have all ably dis- 

 cussed these points ; but the continual 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 preA'ailing ojiinion 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. 



Note.— While this memoir was passing through the press, the Report of Mr. AVhiteaves, F. G. S., Palseouto- 

 logist to the Canadian Survey, on the invertebrate fossils of the I.aramie and Cretaceous of the Bow and Belly 

 River districts apjjeared. (Contributions to Canadian Palaeontology, Vol. i. Part 1, 89 pages and eleven plates). 

 This valuable Report constitutes an independent testimony, based on animal fossils, to the age of the beds in 

 question, and accords in the main very closely with the conclusions above derived from fossil plants. Unfor- 

 tunately, however, no animal remains have yet been found in the Kootanie series, and the only fossil recorded from 

 the Mill Creek beds is a species of Inoceramm, characteristic in the United States of the Niobrara and Benton groups, 

 a position a little higher than that deduced from the plants. 



' Florula Discoana. 



