Cretaceous Floras of Canada. 959 
It isa remarkable phenomenon in the history of the genera of 
plants in the later Mesozoic and Tertiary, that the older genera - 
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 condi- 
tions in the modern ; but it indicates also a law of rapid multipli- 
cation of species in the early life of the genera. The distribution 
of the species of Salisburia, Sequoia, Platanus, Sassafras, Lirioden- 
dron, Magnolia, and many other genera, affords remarkable proofs 
of this. 
Gray, Saporta, Heer, Newberry, Lesquereux and Starkie Gard- 
ner, have all ably discussed 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 prevailing opinion that the 
Miocene was a period of great extension of warmth and of a tem- 
perate flora into the Arctic, must be abandoned in favor 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, 
