324 REVIEWS 



It has long been known that rocks surfer actual molecular move- 

 ment if the forces act so slowly that they do not overpass the elastic 

 limit of the rock, and again bodily movement must take place if the 

 rock is subject to stresses greater than the ultimate strength of the 

 rock, but the knowledge of the fact that solid matter has so much in 

 common with gases and liquids is almost wholly due to the laborious 

 investigations of Professor Spring, and these facts should immediately 

 take their place in our theories of the condition of matter in the inte- 

 rior of the earth. C. F. Tolman, Jr. 



United States Geologic Atlas, Folio jy. Downieville, California. 

 1897. 



This folio consists of eight pages of text signed by H. W. Turner, 

 geologist, a topographic map of the district, a map showing the areal 

 geology, a map showing the economic features, a structure section 

 sheet, and one page of special illustrations. 



The quadrangle represented in this folio lies between parallels 

 39° 30' and 40 ° north latitude, and 12 1° and 120 30' west longitude. 

 It comprises a portion of the northern Sierra Nevada and lies in 

 Plumas and Sierra counties. The area is drained by the forks of the 

 Feather and Yuba rivers. 



The formations are divided into two main groups, the bed-rock 

 series and the superjacent series. The bed-rock series is composed of 

 Juratrias and Palaeozoic sediments and tuffs, and a series of old igneous 

 rocks chiefly granites and porphyries. The Juratrias rocks comprise 

 chiefly the Milton formation which is found only in the southeast por- 

 tion of the quadrangle. The Milton formation, while formed of mate- 

 rials deposited under water, contains a large amount of igneous 

 material. Underlying the Milton formation there are volcanic beds 

 which are likewise presumed to be of Juratrias age, inasmuch as in the 

 lower portion there are lenses of siliceous argillite, in one of which an 

 ammonite was found. These volcanic beds are grouped as quartz- 

 porphyry and as augite-porphyrite. The quartz-porphyry also occurs 

 as dikes. The other igneous rocks forming part of the bed-rock 

 series are granite, gabbro, and granodiorite. In the western portion 

 of the quadrangle there are very large amounts of serpentine which 

 have resulted from the decomposition of the pyroxene olivine rocks or 

 peridotites and amphibolite which is the result of dynamo-metamor- 



