and on the Age of the Cascade Mountains. 177 
tum, ¢, fig. 2 and 8, to Prof. Leo Lesquereux for examination. 
According to this high authority, they consist of leaves of two 
species of oak and one of conifer, and wood of oak and conifer. 
“The species,” he writes me, “mark undoubtedly Miocene or 
uppermost Hocene, more probably the former.”* Therefore I 
conclude the leaf-bearing stratum, c, fig. 2, is certainly Tertiary 
and probably Miocene; and, therefore, the lava flood occurred or 
gan to occur during or after the Miocene. And since the 
upper surface of the conglomerate is itself an eroded land sur- 
face (p. 175), which erosion took place after the period of the 
leaf-bed, the laya-flood occurred more probably after the Mio- 
cene, 
said “began to occur,” for the process of up-building probably 
But on the western an especially on the southern borders of 
the great flood, where the lava thins out, first, occasional ger 
of slate and granite appear as islands above the flood-level, and 
finally the flood itself dwindles into streams flowing about 
€ bases of granite and auriferous slate hills similar to those 
characterizing the Sierra Range. It is true, the sections made 
volume on Fossil 
* A description of these leaves will appear in the forthcoming 
Botany of the Geol. Survey of California. 
