.^80 
The American Geologist. 
December,' ISSfT 
tain a depth already secured. Of 
these two courses the latter seems 
the more reasonable. Any sub- 
sequent filling of this fissure by 
sandstone, shales or loose debris 
would present comparatively 
slight opposition to erosion. 
The Lava Flows. Figure 3 is 
intended to represent a profile 
of the igneous rock surface in- 
cluding the river gorge immedi- 
ately above the elbow at the 
Dalles. The profile is extended 
on the west side of the river to 
the Swedish church at the top of 
the ridge fifty rods south of the 
center of Sec. 25, and on the 
east to the top of the diabase 
cliffs. By this profile it will be 
seen that seven very prominent 
steps constitute the ascent on 
the west side of the river. At 
each step there is a repetition of 
certain easily recognized physi- 
cal and structural characters. 
These characters may be 
grouped as follows : At the sum- 
mit of each step there is a persis- 
tent highly epidotic zone, pos- 
sessing in many cases none of 
the original mineral characters 
of true diabase. Structures re- 
sembling flowage lines are ob- 
servable only in this zone. In 
position and bearing these lines 
correspond closely to the previ- 
ous statements of dip. A more 
persistent lateral plane of sep- 
aration coincides with this zone, 
as will be noted by the wide 
bench leading in each case to the 
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