nif M 



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170 



THE GEOLOGICAL HISTORY OF PLxVNTS. 



Along with this a great cliange was in progress in 

 vegetable and animal life. The flora and fauna of the 

 Paleozoic gradually die out in the Permian and are re- 

 placed in the succeeding Trias by those of the Mesozoic 

 time. Throughout the Permian, however, the remains 

 of the coal-formation flora continue to exist, and some 

 forms, as the Calamites, even seem to gain in importance, 

 as do also certain types of coniferous trees. The Triassic, 

 as well as the Permian, was marked by i)hysical disturb- 

 ances, more especially by great volcanic eruptions dis- 

 charging vast beds and dykes of lava and layers of volcanic 

 ash and agglomerate. This was the case more especially 

 along the margins of the Atlantic, and probably also on 

 those of the Pacific. The volcanic sheets and dykes as- 

 sociated with the Red Sandstones of Nova Scotia, Con- 

 necticut, and New Jersey are evidences of this. 



At the close of the Permian and beginning of the 

 Trias, in the midst of this transition time of physical 

 disturbance, appear the great reptilian forms character- 

 istic of the age of reptiles, and the earliest precursors of 

 the mammals, and at this time the old Carboniferous 

 forms of plants finally pass away, to be replaced by a 

 flora scarcely more advanced, though different, and con- 

 sisting of pines, cycads, and ferns, with gigantic equiseta, 

 which are the successors of the genus Calamites, a genus 

 which still survives in the early Trias. Of these groups 

 the conifers, the ferns, and the equiseta are already famil- 

 iar to us, and, in so far as they are concerned, a botanist 

 who had studied the flora of the Carboniferous would 

 have found himself at home in the succeeding period. 

 The cycads are a new introduction. The whole, how- 

 ever, come within the limits of the cryptogams and the 

 gymnosperms, so that here we have no advance.* 



* Fontaine's " Early Mesozoic Flora of Virginia " gives a very good 

 summary of this flora in America, , . 



1 



