Geology and Natural History. 163 



of l'hyolitic eruptions. The rhyolite was followed by pyroxene- 

 andesite and the eruptions became more and more basic until the 

 close of the volcanic period. The feldspathic and pyroxenic 

 lavas do not approach each other v.\ their tenure of silica within 

 2*25 per cent. In chemical composition the earliest eruptions of 

 both magmas resemble each other, but from this common 

 ground they differentiate steadily until the feldspathic reaches 

 the extreme acidic, and the pyroxenic the extreme basic end of 

 their respective series. The extreme products of differentiation 

 in any volcanic center in the Great Basin are rhyolite and basalt. 



3. Geological Survey of Alabama, Prof. E. A. Smith, the State 

 Geologist, has recently issued a brief sketch of the Geology of Ala- 

 bama, occupying 36 octavo pages. There has been published also 

 Bulletin No. 4, of the Alabama Survey, consisting of a Report on 

 the Geology of Northeastern Alabama and adjacent portions of 

 Georgia and Tennessee, by C. Wileard Hates, Assist. Geol. U. S. 

 G. S., which describes the rocks and the orographic structure of the 

 region, gives figures of the flexures and faults, and closes with 

 an excellent colored map showing the distribution of the Paleo- 

 zoic formations from the Cambrian upward. 



4. Geological Atlas of the United States, Chattanooga sheet, 

 Tennessee. — A large folio brochure, consisting of 6 pages of text 

 and 4 maps, has just been published by the United States Geologi- 

 cal Survey. The maps include a topographical map of the region, 

 two detailed geological maps in colors, and one sheet of sections. 

 The area represented covers about f 00 square miles. The size of 

 the maps is 14^ by 17-j inches. The work is in the best style as 

 regards the exhibition of the geological formations, and is also 

 faultless esthetically. The charts are the commencement of a 

 series, already far advanced as regards geological investigation, 

 which has in view the representation of the geological structure 

 of the Appalachian region. The names of the geologists men- 

 tioned on the charts are G. K. Gilbert, Chief Geologist, Bailey 

 Willis, Geologist-in-charge, and Geology by C. Willard Hayes. 



5. The North American Continent during Cambrian Time, 

 by C. D. Walcott. From the 12th Report of the Director of 

 the IT. S. Geological Survey, for 1890-91, pp. 529-568. — Mr. 

 Walcott here exhibits in an instructive way by maps and descrip- 

 tions his results as to the geographical condition of Cambrian 

 North America. 



6. The Lafayette Formation, by W. J. McGee, Ibid., pp., 

 351-521. — This paper is a very full exhibition of the characters 

 and distribution of the Lafayette formation. The latter subject 

 is presented on a colored geological map, which exhibits also the 

 author's views as to the distribution of the Columbian formation. 



7. The Origin and Nature of Soils, by N. S. Shaler, Ibid, 

 pp. 217-346. — Professor Shaler considers the subject of soils from 

 a geological point of view. The sources of soils are explained, 

 their various characteristics, the processes by which they have been 

 formed over regions of diverse conditions, and the geological 



