The Siskiyou Island. 51 



In the deposits of sediments along the in- 

 ner slopes of this basin, the changed remains 

 of which now border the Willamette valley 

 as thick beds of rock, aggregating in some 

 localities hundreds of feet in vertical thickness, 

 may be traced the progress of this Miocene 

 work, in many places marked by abundance of 

 marine shells in the very sands and mud flats 

 in which they lived, but all now changed to 

 rock. Time has worn away the less dense 

 surface layers of this varied deposit, but the 

 denser lower layers of it have in different de- 

 grees resisted this wear and formed the foot 

 hills in nearly the entire circuit of the present 

 valley from the Columbia river to the Cala- 

 pooia mountains. 



A fine exposure of these Miocene sedi- 

 ments may be seen in the excavated streets 

 of Astoria, resting on a like exposure of the 

 underlying Eocene, both groups of fossils 

 finely preserved, often enclosed in concretions 

 which apparently formed around the decay- 

 ing shells in quiet, deep waters. Sometimes 

 the enclosed fossil is a crab, and in the shales 



