ECOLOGICAL SIGNIFICANCE OF EAGLE CREEK FLORA 585 
favor the wide scattering of the leaves which fell upon it, there is 
the added feature that the thick xerophytic leaves alone would be 
strong enough to undergo transportation without being destroyed. 
Surely we must assume that the perfect specimens of maple, 
sycamore, and other broad thin leaves were not transported far 
from the spot where they first fell. Further, the large number of 
mesophytic species associated with the dominant maple and elm 
leaves indicates that the deposits containing them were laid down 
in the valley where they grew. 
The evidence of the plant fossils thus may be explained on the 
basis of a twofold habitat such as would be furnished by an upland 
region traversed by valleys. Whether or not this hypothesis is 
supported by the geological evidence may be determined by a con- 
sideration of the physical conditions which existed during the 
Eagle Creek epoch. 
PHYSICAL CONDITIONS DURING THE EAGLE CREEK EPOCH 
The Eagle Creek formation is made up entirely of volcanic 
materials. In the lower part, as exposed at Red Bluffs, beds of 
tuff and ash are most conspicuous; above, the activity of streams 
is evidenced by the predominance of conglomerate. Thus it is 
clear that early in the epoch vulcanism was the dominant process 
but that toward the close the streams were able to carry and assort 
the volcanic material as fast as it was ejected, as well as erode the 
lava flows bordering the craters. This sedimentary phase is the only 
one represented on the Oregon side of the gorge and is the source 
of practically all of the fossil plants. 
There are several conspicuous features, applying especially to 
the conglomeratic phase, which require analysis. In the first 
place there is a predominance of coarse material—rounded bowlders 
ranging up to 15 feet in diameter and averaging from 1 to 3 feet. 
The textural range is high in any outcrop, large bowlders mingled 
with small, all bound together by a matrix which varies from coarse 
gravel to fine mud, but is commonly sandy in texture. The abun- 
dance of large bowlders and the almost entire lack of assortment 
point to the deposition of these sediments by streams which had 
high velocity. 
