THE BALD CYPRESS 63 



During the late Tertiary time which succeeded the Miocene, 

 termed Pliocene by geologists, North America again furnishes us 

 with but few plant beds. The available deposits of this age on 

 this continent are marine shell marls without plant fossils or interior 

 basin deposits with vertebrate fossils in regions of increasing aridity 

 like the western plains or mountain basins, apparently too dry for 

 the cypress. Along our Gulf coast in what is known as the Plio- 

 cene Citronelle formation, a series of sands and muds, deposited 

 in lagoons along the sea coast, there occur abundant remains of 

 twigs, cone scales and seeds of a cypress indistinguishable from 

 our existing bald cypress. 



In Pliocene Europe on the other hand, there are preserved many 

 plant beds of this age and the cypress was apparently one of the 

 most common denizens of the shores of the greatly expanded Medi- 

 terranean Sea, which at that time spread over southern Europe and 

 eastward into Asia. The accompanying sketch map of the world 

 shows graphically the areas occupied by the existing cypress (in 

 soHd black) and the approximate area over which it extended its 

 range during Tertiary times (lined areas). 



At the close of the Tertiary the long period of more or less wide- 

 spread equable climates was broken by those climatic changes 

 which inaugurated the extensive glaciation of the Pleistocene. Our 

 records of Pleistocene plant migrations are much scantier than one 

 might wish, but we know that the cypress along with a great many 

 other Miocene forest types became exterminated in Europe by 

 reason of the vicissitudes caused by the repeated ice sheets that 

 spread outward from the Scandinavian highlands and from the 

 higher mountain masses farther south. Why the cypress did not 

 survive in southeastern Asia is a mystery and perhaps it will even- 

 tually be found in the not yet thoroughly explored upland valleys 

 of southern central China — a great plant refuge where recently 

 have been discovered the hickory, sassafras and tulip-tree, and many 

 other plants like magnolias, maples and ashes that serve to em- 

 phasize the long known and very striking paralleHsms between 

 the existing floras of southeastern Asia and southeastern North 

 America. 



