1893,] Cretaceous Plant Population. 345 
contributed to this condition. The older types of plants, 
making up the bulk of the forest, were isolated from the shores 
and from the banks of streams, except very far inland. Con- 
sequently their remains are preserved only under exceptional 
conditions. That the metaspermic plants occupied the 
tension-line position indicates the preponderance of older types 
in the great inland stretches of country. The rapid appear- 
ance of new metaspermic types during the Cretaceous—and 
probably too in Jurassic time—was a result of the tension-line 
position into which they had been forced. The high develop- 
ment of the arboreal habit may be referred to similar causes. 
The picture thus brought before the eyes differs much from 
the usual reconstructions of Cretaceous landscapes, but may be, 
nevertheless, a closer approximation to the truth. A final 
word may be added in regard to the conditions of the Triassic 
and even of earlier time. In those ages we may imagine the 
metaspermic types developing in the ancient forests of cycads 
—or even of Lepidodendrons and Annularias—and beginning 
their forced marches to the peripheral regions of the solid, 
archaic formations of their birth. Thus for century upon 
century they may have existed, and fail to appear in the fos- 
sils, because of their internal position in the formations. But 
when, after their long struggle for food and light and soil for 
support, they emerge upon the periphery of their parent for- 
mations we find them already arborescent or arboreal, and soon 
almost universal upon littoral areas. They then first come 
into a position where preservation in the rocks is possible. 
