776 GEOLOGY 



have been recognized in Alaska (Krnni series) where they are coal- 

 bearing in places. 



The Eocene system has tin estimated thickness of 10, ()()() to 

 12,000 feet in southern Oregon, and but little less in southern 

 California. 



After the Eocene, there was a time of temporary elevation, 

 erosion, and volcanic activity along the Pacific coast, with con- 

 siderable basaltic flows in Washington and Oregon. 



The western interior. The warpings, faultings, and the intru- 

 sions and extrusions of lava which marked the close of the Meso- 

 zoic era in the west appear to have developed lands which were 

 relatively high, adjacent to tracts which were relatively low. The 

 steep slopes of the mountain folds, fault scarps, and volcanic piles 

 seem to have afforded the conditions for rapid erosion, while the 

 adjacent lowlands furnished places of lodgment for much of the 

 sediment. Some of it took the form of fans and alluvial plains, 

 and some of it probably lodged in lake basins formed by warpin.ii;. 

 or by the obstruction of valleys by lava flows. The wind also made 

 its contribution to the deposits of the time. The result was an in- 

 extricable combination of fluvial, pluvial, eolian, and lacustrine 

 deposits. Deposition on land was therefore a feature of the period. 

 as of all subsequent time, and among the accessible formations of 

 this and later periods, those of terrestrial origin are more wide- 

 spread than those of marine origin. 



The sites of principal sedimentation shifted somewhat from 

 time to time, and among the widely distributed deposits referred 

 to this period, there are great differences of age. Several more <>r 

 less distinct stages of deposition have been made out, the distinc- 

 tions being based partly on the superposition of the beds, and pail ly 

 on their fossils. 1 These several stages are not readily correlated 

 with those of the coasts. 



1. Reference has already been made to certain formations 

 which have been classed commonly as Cretaceous, which should 

 probably be regarded as early Eocene (p. 752). Some of t! 



1 For an account of the deposits near the lOili parallel, seo Kind's report, 

 Vol. I, already cited. For an attempt at correlating the several formations, 

 see Ball, 18th Ann. Kept., U. S. Geol. Surv., Pt. II; also J. II. Smith, Jour. 

 Geol., Vol. VIII, pp. 444-471. 



