SALIENT FEATURES OF THE GEOLOGY OF OREGON loi 



plains. This level is recorded in the major valleys by a prominent terrace 

 developed mostly in the Satsop formation but in places cut in the underlying 

 basalt. This is the Cowlitz Terrace already described. 



The uplands of this Satsop plain bear a red clay soil 10-15 feet deep. This 

 grades down into a much-decomposed gravel. At a depth of 30 feet the 

 pebbles are decayed only on the exterior. Below 50 feet most of the material 

 is hard and ringing when struck with the hammer. Near the Columbia the 

 clayey residual soil on the top of the Satsop formation contains scattered quartz- 

 ite pebbles, hard, bright, polished, and apparently unaffected by the weather- 

 ing which has reduced the associated basaltic pebbles to a structureless clay. 



The present writers have examined this formation along the 

 Sandy and the Columbia rivers near Crown Point, but have not 

 traced it over anything Hke the territory covered by Bretz. Wher- 

 ever they have seen it the formation appeared to be an ordinary 

 river gravel plastered against the sides of the valleys and on benches 

 above the present stream beds. We did not see it disappear under 

 the andesitic lavas at any point, though we are not prepared to say 

 that is may not do so. A deposit of gravel might very easily be 

 laid down underneath an undercut cliff and in this way give one the 

 impression of having been laid down first, with a lava flow rolling 

 out on top of it later. 



With these river gravels Bretz correlates, by taking a long jump, 

 the gravels already referred to, occurring at Cape Blanco and 

 Elk River. He also suggests the inclusion of the quartzitic gravels 

 in eastern Oregon at The Dalles. Why not go farther east to the 

 John Day country, where the Rattlesnake formation (Pliocene) is 

 found to contain many quartzitic pebbles! As yet no fauna has 

 been found m these Cascade gravels. 



Fossil leaves were found in this formation by J. B. Winstanley, 

 of Portland, and collections were made by R. W. Chaney, of the 

 University of Chicago. Of these I. Williams,' in his Columbia 

 Gorge paper, says: 



The fossil horizon is exposed three-fourths of a mile back from the Sandy 

 River road, in the south side of the canyon of Buck Creek 25 feet above the 

 water, beneath an overhanging cliff of conglomeratic phase in which pebbles 

 of polished quartzite are common. Mr. Chaney states that in this one exposure 

 of the Satsop, four genera and at least seven species of plant life are represented. 



' I. Williams, Ore. Bur. Mines and Geol., II, No. 3 



