ECOLOGICAL SIGNIFICANCE OF EAGLE CREEK FLORA 587 
conspicuous. On the Oregon side, farther away from the supposed 
range, the amount of pyroclastic material is relatively incon- 
spicuous, as might be expected at a distance of 6 to 8 miles from the 
range. 
It may be suggested that the 500-foot section of conglomerate 
on the Oregon side of the gorge represents the upper conglomeratic 
portion of the Red Bluffs section, and that the ashy and tuffaceous 
lower portion lies below. Surely the southward dip of the over- 
lying basalt makes this explanation of the variation in thickness 
plausible. On the other hand, it appears reasonable to suppose 
that the 500 feet exposed on the Oregon side represents more than 
Red Bluffs 
i Bonneville 
Fic. 4.—Showing the possible relations of the Eagle Creek formation on the 
flanks of a volcanic peak or range. The dashed line indicates the present position 
of the Gorge of the Columbia River in cross section. ; 
the upper 500 feet of the Red Bluffs section. There are more 
intrusions in the latter, as might be expected at a point nearer the 
mountain range. And the paucity of plant remains in the con- 
glomerates of Red Bluffs also has significance when it is realized 
that the proximity to volcanoes would probably be unsuitable 
for the growth of vegetation. It is of course possible that were the 
upper part of the Eagle Creek section readily accessible for study, 
plant-bearing lenses might be found in abundance there; but in 
all of the talus material examined at the foot of the cliffs only two 
masses contained leaf impressions, and these but few. The varia- 
tion in thickness of the formation from north to south may then 
be due to a greater or less extent to the distance from the range 
constituting the source of the sediments. 
In summary, the lithological characters of the Eagle Creek 
formation—its coarseness, lack of assortment, and lens and pocket 
stratification—point to the origin of the conglomeratic layers as a 
