718 



SCIENCE. 



[N. S. Vol. I. No. 2G. 



but little effort lias been made by California 

 to elucidate her economic geology, notwith- 

 standing the liberal appropriations which 

 the State Legislature makes regularly for 

 the maintenance of a so-called ' Mining- 

 Bureau.' In the knowledge of her geologic 

 resources, California is far behind many 

 minor States of the Union. It is therefore 

 fortunate that the Federal authorities have 

 so steadily prosecuted the inquiry into the 

 geology of the gold belt of the Sierra 

 Nevada and of other portions of northern 

 Cahfornia. The sheets under review are 

 the results of this work. They fomi part 

 of the geologic atlas of the United States 

 and they are among the first dozen of the 

 entire series. The mechanical execution of 

 the folios challenges the admiration of all 

 familiar with such work. In the opinion 

 of the writer they compare very advantage- 

 ously with the best European efforts of a 

 similar kind. It is gratifying to American 

 pride to see the beginnings of so vast a 

 scientific project as a geologic atlas of the 

 United States realized in a manner so emi- 

 nently satisfactor}^ If there exists a doubt 

 in the minds of the geologists of the countrj^, 

 and in this case the geologists speak for the 

 people, as to the ultimate success of the 

 project, it is based on the fear that there 

 may not be in the future, as there certainly 

 has not been in the past, a proper coordina- 

 tion of the topographic and the geologic 

 branches of the survey. A correct topo- 

 graphic base is the sine qua non of a good 

 geologic map; and unfortunately the topo- 

 grapher's conception of a correct map, in 

 the present state of his professional educa- 

 tion, is not what it ought to be. Thorough 

 and conscientiously executed topographic 

 surveys are expected of the geological sur- 

 vey. The ambitious extension of the topo- 

 graphic surveys far in advance of geologic 

 investigation, at a rate Avhich not only abso- 

 lutely precludes the possibility of thorough 

 work but demoralizes the topographer, can 



only bring serious discomfiture to the Geo- 

 logical Survey as a government institution. 



The Sacramento, Placerville and Jackson ■ 

 folios bring out clearly the salient features 

 of a section ^vhich may be taken as typical 

 for the Avestern slope of the Sierra Nevada. 

 The Sierra slope rises from the eastern edge 

 of the Great Valley of California to the 

 crest of the range, some 60 miles distant at 

 an inclination of less than 2°. It presents the 

 chai'acters of a gently tilted plain which 

 has been incisivelj^ dissected by the streams 

 which traverse it. This slope is underlain 

 by two very difierent assemblages of rocks. 

 The first of these is composed of sediment- 

 arj' and eruptive formations which have 

 been intensely disturbed, metamorphosed 

 and invaded by vast intrusions of granitic 

 magma, forming a complex whose eroded 

 stirface serves as the basement upon which 

 the second assemblage reposes in little dis- 

 turbed attitudes. The older assemblage is 

 designated in the folios the ' Bed-rock ' se- 

 ries, and the newer, the ' Superjacent ' se- 

 ries. ISTeither of these terms is felicitous, 

 although the first is based on popular usage 

 and will appeal to the mining community. 

 The Bed-rock series comprises the rocks 

 which are known popularlj' as the aurifer- 

 ous slates, together with their associated 

 eruptives and irruptives, and also the gi'an- 

 itic rocks which invaded the series as a. 

 whole at the close of the Jm-assic. It would 

 be better if these granitic intrusions were 

 not classed in the same category with the 

 auriferous slates as part of a ' series.' The 

 auriferous slates comprise the Calaveras for- 

 mation (Carboniferous, with possibly some 

 older Paleozoic) and the Mariposa forma- 

 tion. In the earlier Sacramento and Pla- 

 cerville folios, which are chieflj' Lindgren's 

 work, the Mariposa formation is colored as 

 Cretaceous, while in the later Jackson folio- 

 by Turner the same formation is colored as 

 Jurassic. The reference of this formation 

 to two difierent horizons can scarcely be 



