THE PLEISTOCENE OR GLACIAL PERIOL. 



477 



By far the larger part of the marine Quaternary deposits of the coasts 

 of the continent are still beneath the sea. As interpreted by the 

 marine fossils, the climate of that portion of the Pleistocene in southern 

 California which is represented by these marine stages, was distinctly 

 warmer than that of the Pliocene; l but this does not apply, probably, 

 to any large part of either period. 



Igneous recks. — The late Tertiary eruptions of North America 

 have not everywhere been clearly separated from those of the Quater- 



Fig. 560. — A floated crag of scoria, in recent lava-flows, Cinder Buttes, Ida. 

 (Russell, U. S. Geol. Surv.) 



nary period, but there are in numerous places igneous rocks which are 

 clearly post-Tertiary, some of them even late Quaternary. Some of 

 these very young igneous rocks have been referred to in connection 

 with the history of Lakes Bonneville, Lahontan, and Mono, but they 

 are by no means confined to the bas'ns of these lakes. Mount Shasta 

 shows several post-glacial lava-flows, 2 and there are small cinder- 

 cones on alluvial cones at the east base of the Sierras in southeastern 

 California. 



1 Fairbanks, Jour, of Geol., Vol. VI, p. 566. 



2 Diller, Physiography of the United States, pp. 245 et seq. 



