1913-] STRATIGRAPHY OF PACIFIC COAST OF AMERICA. 599 



sloping floor of successive basaltic flows and tuffs. In the Cascade 

 Mountains intercalated sediments are reduced to a minimum but 

 farther to the west and south they apparently replace more and more 

 the igneous materials. With the close of the Tejon this floor was 

 elevated into the form of a plateau with a synclinal sag at the 

 present position of the Willamette Valley. At the opening of the 

 Astoria period of sedimentation an arm of the sea extending up the 

 Willamette Valley at least as far as Eugene connecting across the 

 Range at Wren and Blodgett but it was not until the Seattle Epoch 

 that the Coast Range was completely submerged by the load of 

 igneous and sedimentary detritus piled upon it, for at many points 

 on the west flank particularly near Nehalem and Tillomook Harbors 

 the Seattle beds rest directly on the Eocene with the lower Astoria 

 (San Lorenzo) lacking. Following this, western Oregon was elevated 

 and except for an embayment of the Monterey sea which extended 

 up the Columbia River and southward to the Tualatin Valley west of 

 Portland, no later sediments have been deposited inland from the 

 extreme western border. It is probable that the coast line has stood 

 near its present position during much of late Tertiary time owing 

 to the existence of an important fault paralleling the coast for many 

 miles. Elevations on the east side of this fault have resulted in the 

 removal of all the later and much of the early Tertiary deposits and 

 submergences on the west side have carried the successive deposits 

 even deeper beneath the sea. 



Much has been written of the continuity of the Willamette 

 Valley with the geosynclinal trough of the Great Valley of Cali- 

 fornia, but facts do not bear this out. The Willamette Valley is 

 the result of the differential erosion of soft shales and sandstones 

 compared with the basalts which flank it. It is underlain at no great 

 depth by Eocene deposits, igneous and sedimentary, which frequently 

 stand up as monadnocks through the thin veneer of fluvial deposits 

 and alluvium. The so-called " Willamette Sound " either refers to 

 the Oligocene embayment or to the fluvial deposits in the Willamette 

 Valley above Oregon City where a late Tertiary basalt flow impinged 

 in passing down the lower Willamette and Columbia Rivers and 

 temporarily dammed back the Willamette River. 



