3l6 ABSTRACTS: GEOLOGY 



GEOLOGY. — Relation of landslides and glacial deposits to reservoir sites 

 in the San Juan Mountains, Colorado. Wallace W. Atwood. 

 U. S. Geol. Survey Bull. 685. Pp. 38, 8 plates, 17 figs. 1918. 



Inasmuch as experience has shown that many landslide masses and 

 certain of the glacial deposits are not able to withstand the pressure of 

 a high head of water without serious leakage, it seems desirable to pub- 

 lish a description of the mountain canyons and the deposits commonly 

 found in them and of the geologic conditions associated with the lakes 

 in the mountains, so that, in the future, no expensive errors need be 

 due to a failure to recognize the geologic formations bordering a pro- 

 posed reservoir site. Glacial deposits of the Wisconsin glacial stage are 

 described in detail. Landslides and torrential deposits in larger canyons 

 are discussed. Several reservoirs are described and illustrated in de- 

 tail. R. W. Stone. 



GEOLOGY. — Geology and ore deposits of the Tintic mining district, 

 Utah. Waldemar LindgrEn and G. F. Loughlin, with a historical 

 review by V. C. Heikes. U. S. Geol. Survey Prof. Paper No. 107. 

 Pp. 282. 39 plates, 49 figures. 1919. 



The report gives the result of a detailed re-survey of the Tintic dis- 

 trict, results of the first survey by G. W. Tower, Jr., and G. O. Smith 

 having appeared in the nineteenth annual report of the Survey in 1898. 

 The scope of the report is similar to that of other Survey professional 

 papers on mining districts, and particular attention may be directed to 

 the following feattues: 



Part I (by G. F. L.): — Revision of the stratigraphy based on newly- 

 discovered paleontologic evidence, proving the existence of lower, 

 middle, and upper (?) Cambrian, lower and upper Ordovician, upper 

 (?) Devonian, and Mississippian strata; unconformities at the base of 

 the Ordovician and of the Mississippian; description and correlation 

 of igneous rocks, including early latite or andesite, early and late rhyo- 

 lites, later latites and monzonite, and basalt; magmatic differentiation 

 of the igneous rocks, comparing evidence for and against magmatic 

 stoping, abyssal and marginal assimilation; folding and faulting, the 

 latter taking place during 5 periods; rock alteration considered under 

 three heads: (a) before volcanic activity (formation of chert, dolomite, 

 and some sericite, and prevolcanic products of weathering) ; (6) during 

 and immediately after volcanic activity; {c) distinctly later than vol- 

 canic activity. 



