600 ARNOLD AND HANNIBAL— MARINE TERTIARY [April 19, 



The Chehalis Valley and Southwestern Washington. 

 The geologic history of this district during the Tertiary has been : 

 first the deposition of the Tejon series chiefly as an estuarine deposit 

 but with some associated lavas, mostly basalts ; second the defor- 

 mation of Tejon by folding in a west-east or northwest-southeast 

 direction; third the successive deposition of the Astoria Series, and 

 the Monterey, Empire, and Merced formations ; fourth the final 

 elevation of the Olympic and Cascade Mountains in Pliocene time 

 and the resultant faulting, prevailingly in an east-west or north- 

 south direction, of all the Tertiaries of southwestern Washington 

 into a jumble of westward-dipping monoclinal blocks. Except locally 

 in the proximity of faults, folding of the Oligocene and later strata 

 of Washington is almost unknown. 



The Tertiaries of the Periphery of the Olympic Complex. 



The succession of events about the periphery of the Olympic 

 complex is similar to that of southwestern Washington, except that 

 the Tejon is very largely absent and the folding which succeeded 

 it has left no record. On the west coast several isolated areas of 

 Tertiary rocks have been faulted down into the Cretaceous, and 

 thus preserved. A fault which requires special mention in this con- 

 nection is the one which marks the north boundary of the Olympic 

 Mountains, extending from the mouth of the Soo-es River south 

 of Cape Flattery to Lake Crescent and the head of S'quim Bay 

 an unbroken distance of more than eighty miles. On the south side 

 except at the terminii all the adjacent rocks are pre-Tertiary. To 

 the north lies the great monocline of northwestward-dipping Oligo- 

 cene beds. It is probable that a second fault paralleling this lies 

 in the trough of the Straits of Fuca else it is difficult to explain 

 that remarkable topographic feature. The structure of the gently 

 seaward-dipping Tertiary rocks of the southwest coast of Vancouver 

 Island may also be readily explained by an assumption that such a 

 fault exists. 



Puget Sound is probably a pre-Pleistocene valley of erosion filled 

 by glacial debris. It has been regarded as a structural depression, 



