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 



Fig. 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 



