ILLUSTRATIONS 
Page. 
Plate I. Sketch map of southwestern Idaho and southeastern Oregon 8 
II. A, South shore of Malheur Lake, Oregon, Salacornia growing in 
alkali; B, Eolian mounds on border of play a near Iron Moun- 
tain, Oregon _' 30 
III. A and B, Crags of tuff on lava flow, Cinder Buttes, Idaho 38 
IV. A, Island of lapilli in lava stream, Cinder Buttes, Idaho: B, 
Scoria and bomb cones, ' ' The Ice Wells/ ' Cinder Buttes, Idaho _ 40 
V. Volcanic bombs, Cinder Buttes, Idaho 40 
VI. Volcanic bomb, Cinder Buttes, Idaho 42 
VII. Volcanic bombs, Cinder Buttes. Idaho 42 
VIII. Volcanic bomb, Cinder Buttes, Idaho 42 
IX. Sections of vesicular volcanic bombs _ 44 
X. A, Cracked surface of volcanic bomb, Cinder Buttes, Idaho; B, 
Fragment from a cinder cone, showing dense portion due to 
hardening of splashes of liquid lava, Cinder Buttes, Idaho 44 
XI. A, Driblet cone or "oven," Jordan Craters, Oregon; B, Driblet 
cone. Diamond Craters, Oregon 52 
XII. A, Fissured pahoehoe lava, Jordan Craters, Oregon; B, Aa lava 
surface, Cinder Buttes, Idaho 58 
XIII. A and B, Margins of lava flows, Cinder Buttes, Idaho 58 
XIV. A and B, Lava gutters, Jordan Craters, Oregon _ __ 60 
XV. A, Pressure domes in recent lava, Jordan Craters, Oregon; B, 
Pressure ridge in recent lava. Diamond Craters, Oregon 60 
XVI. A and B, Weathering of rim rocks of basalt above soft terranes. 60 
XVII. A and B, Exposures of volcanic dust of Tertiary age near Beulah, 
Oreg 62 
XVIII. A and B, Exposures of Tertiary lake beds, Owyhee River, Oregon _ 62 
Fig. 1. An ideal geological section illustrating the manner in which petro- 
leum and natural gas accumulate in anticlines, and also the origin 
of hydraulic pressure on such ' ' pools " 74 
2. An ideal geological section illustrating the manner in which petro- 
leum and natural gas may be concentrated in horizontal beds 75 
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