214 RECORD OF SCIENCE FOR 1886. 



Susquehanna anticlinal. These lower rocks are more perfectly crystal- 

 line and contain a greater proportion of muscovite and feldspar than 

 the upper series into which they graduate, and which are magnesian, less 

 crystalline, and possibly of Paleozoic age. Tbe quartzites of Chikis, 

 Chester Valley, etc., are thought to be Potsdam from their unconformity 

 to the underlying schists.* 



PACIFIC COAST. 



77. Two systematic geologic surveys are now in progress in the State 

 of California, one by Becker, at present in the southern part, and the 

 other by Diller, on the volcanic geology. Some of Becker's results are 

 given in a paper which is referred to at length under " Metamorphism 

 and Paramorphism," and announces the Neocomian age of a portion of 

 the crystalline schists of the Coast ranges. 



Diller makes a preliminary report of progress of work in the northern 

 part of the State, which throws much light upon its geologic history. 

 It is found that the Carboniferous limestones are quite widely distrib- 

 uted and probably embrace all those of the metamorphic rocks. Gil- 

 bert's suggestion that the Sierra Nevada has the basin-range structure 

 is verified, and three westward-sloping blocks are recognized. The age 

 of the auriferous slates is considered doubtful ; while one portion of 

 them is certainly Mesozoic, another portion is apparently older than the 

 Carboniferous limestone, and is, perhaps, altogether pre Carboniferous. 

 The great displacements forming the Sierra Nevada appear to have be- 

 gun about the close of the Tertiary, and may still be in progress. The 

 distribution and relations of the Chico group indicate that during the 

 Chico epoch much of what is now the Coast Range region in northern 

 California was an island separated from the continental mass to which 

 the Sierra belonged by a strait which has since been filled by Lassen 

 Peak lavas to form a portion of the present Cascade Range.t 



78. Le Conte discusses the time of the elevation of the Sierra Nevada 

 from the evidence afforded by the river beds in middle California. In 

 that district the lava flows at the end of the Tertiary were only of suf- 

 ficient thickness to fill up the river channels and cause them to shift 

 their courses to the divides. Previous to this the base-level of erosion 

 had been almost attained, and since the lava flows there has been a 



. great uplift, which has canned the rivers to cut the deep, narrow gorges 

 in which they now run. This idea of post-Tertiary uplift in the Sierra 

 Nevada is interesting in connection with Button's study in the plateau 

 country, where the elevation took place approximately at the same time, 

 and was similarly attended by faulting and great lava flows. According 

 to studies of Gilbert and Eussell on the faults of the Great Basin, uplift 

 in that region appears to have begun in the beginning of the Quater- 



* Am. Phil. Soc, Trans., vol 23, pp. 391-410, and map. 

 tU. S. Geol. Survey, Bulletin No. 33 (vol. 5, pp. 369-387). 



