CRETACEOUS PERIOD 113 



Under the stress of climate and inter-competition these 

 vigorous growths had shown wonderful and varied resources 

 notably in the formation of deciduous habits. The power 

 of adaptation, however, has its limits ; and, owing to the 

 increasing severity of climate, a time came when the various 

 species had for self-preservation to migrate to lower latitudes. 

 In the early Cretaceous there were distinct signs on North 

 American scenes of such migration. Here and there south of 

 Canada growths leaved like fig-trees, willows, sassafras, and 

 magnolia were reconnoitring ; and as time went on, primitive 

 forms of oaks, poplars, birches, and other deciduous growths 

 joined the movement. Progress was necessarily slow. Every 

 inch of ground was more or less disputed by old-established 

 vegetation ; and the emigrants themselves naturally com- 

 peted with one another. But the new types pressed steadily 

 on, enlivening the landscapes with brighter foliage, and 

 greater display of flower. And so successful was the advance 

 that, in the course of the long Cretaceous years, they became 

 in some districts the dominant form of vegetation. " Horse- 

 tails " struggled on, and with some success, in their swampy 

 holdings ; but conifers and cycads the latter especially 

 disappeared from many long-tenanted positions. The most 

 progressive cycads (Bennettitece), that had given promise in 

 their well-protected seeds of plants of higher type than cycads 

 and conifers, (and, so far as is known, the nearest in develop- 

 ment to the new vegetation) became extinct long before the 

 close of the Period. 



This invasion rather brings to mind the northern bar- 

 barians moving down on the Roman Empire. These Creta- 

 ceous hordes, however, were not barbarians of their kind. 

 They were true angiosperms, and in the advanced methods 

 they had developed for the production and welfare of their 

 seeds, they illustrated more strongly than any earlier growths 

 the principle of parental care. 



In the early portion of the Cretaceous Period, though 

 somewhat later in time than in North America, some primitive 

 oaks, planes, and other angiosperms made their appearance 

 in what is now known as the Spanish peninsula. How the 

 seeds whence they sprang reached that territory whether 



