580 RALPH W. CHANEY 
feet at Red Bluffs on the Washington side to 500 feet on the Oregon 
at Bonneville, a condition which appears to be due in part at least 
to the southward plunge of the fold. 
The formation as exposed on Table Mountain and Red Bluffs 
comprises a series of beds of tuff, ash, and volcanic conglomerate, 
the conglomerate being most conspicuous near the top. In several 
of the talus masses of the conglomerate poorly preserved leaf 
impressions are found, and in both the conglomerate and the 
tuff silicified wood is common. To the west of Red Bluffs cliffs of 
conglomerate are conspicuous, and from them have slumped the 
great masses of rock which have dammed the Columbia River, 
resulting in its cascades. The base of the formation is reached 
neither on the Washington nor on the Oregon side. 
On. the Oregon side the maximum section exposed, 500 feet 
thick near Bonneville, is a volcanic conglomerate, in most places 
highly indurated. All the bowlders are of porphyritic basalt, some 
of them reaching a diameter of 15 feet and averaging from one to 
three feet in the coarser phases of the formation. The matrix is 
a fine to coarse volcanic sand. Numerous pockets and lenses of 
shale and sandstone are a characteristic feature. These are of 
slight extent both vertically and horizontally, and in many cases 
contain more or less well-preserved leaf impressions. Silicified 
logs and carbonized stems and fragments are of common occurrence, 
representing driftwood deposited with the sediments. 
The frequence of volcanic activity during the deposition of the 
sediments is indicated by the seams of volcanic ash which are seen 
to overlie some of the soil layers representing old surfaces. A 
quarter of a mile east of Bonneville occurs what is most probably 
a contemporary extrusion of basalt, and on Greenleaf Creek the 
sedimentaries are intruded by basalt. In these situations and else- 
where locally the beds have been contorted and shattered, with the 
development of slickensided surfaces and contact metamorphism. 
The upper surface of the Eagle Creek formation, overlain by 
basalt flows, is markedly irregular, as first noted by LeConte in the 
canyon of Tanner Creek.t| Evidences of intraformational uncon- 
formities are numerous and will be discussed below. 
‘Op. cit. 
