SALIENT FEATURES OF THE GEOLOGY OF OREGON iii 



swampy conditions now indicated by seams of coal. Volcanic 

 activity again broke forth, producing basaltic and diabasic masses, 

 some of which still form conspicuous heights of the northern Coast 

 Range. 



The Klamath region was being still lowered by erosion, and 

 fluvatile and lake deposits equivalent in part to the lone Eocene 

 were formed in local basins. Along the western flanks of the Blue 

 Mountains considerable thicknesses of rhyolitic ash and andesitic 

 flows of the Clarno Eocene suggest the presence of volcanic vents 

 to the westward. Still farther east along the Idaho-Oregon bound- 

 ary local changes in drainage, due perhaps to blocking of channels 

 by lava flows, or faulting, caused the deposition of the stream and 

 lacustrine deposits of the Payette. These terrestrial beds give 

 evidence of a tropical flora the remains of which, accumulating in 

 various terrestrial and estuarine basins of the state, have since 

 changed to the valuable coal seams of the Pacific Coast. 



Only slight deformative movements intervened between the 

 Clarno Eocene and the John Day Oligocene of eastern Oregon, but 

 in the southwest an uplift occurred at the close of the Eocene that 

 inaugurated the conditions which during the two succeeding geologic 

 periods produced the Klamath peneplain. In the meantime the 

 Eocene marine sediments had been gently folded, and the north- 

 western portion of Oregon was again depressed, allowing the Oligo- 

 cene sea to reach the region of the present site of the Cascades and 

 extend southward at least to Eugene. Near the shore of this sub- 

 tropical sea tuffaceous deposits indicate volcanic activity to the 

 eastward. Similar activity is conspicuously represented in some 

 of the tuffs of the John Day Oligocene, which may be in part the 

 correlative of marine Oligocene. The terrestrial deposits of the 

 John Day, according to Merriam, were formed along the flood 

 plains of an old-age stream. These lowlands were the habitat of 

 oreodons, primitive dogs, saber-tooth cats, rhinoceroses, three- 

 toed horses, and numerous other forms well known through the 

 classical studies made upon this fauna. 



The marine Oligocene was deformed, to an extent as yet unde- 

 termined, before the advance of the less extensive Monterey Sea. 

 These waters were still warm, possessing a fauna similar to that of 



