376 He views — CliamherUn and Salisburi/s Geology — 



The chapter (v, pp. 232-308) on "The Work of Snow and Ice" 

 contains much int'ornmtion that has not hitherto filtered into 

 geological textbooks, and is embellished, both pictorially and 

 verbally, with the results of the authors' personal observations in 

 North Greenland. We note that the thickness of the Greenland ice- 

 dome at its centre is estimated at 5,000 feet or more, and we 

 recommend the statement to the attention of the writer in this 

 Magazine (March, 1906, p. 120) who has recently, on hypothetical 

 grounds, revived the idea that ice cannot attain a greater thick- 

 ness than about 1,600 feet. The discussion of the physics of 

 ice-movement in this chapter contains much new and suggestive 

 matter. 



" The Work of the Ocean " is dealt with in chap, vi (pp. 309- 

 374), and this, we think, is one of the weaker chapters of the book. 

 In adhering to tlieir plan of selecting pictorial illustrations chiefly 

 from American sources, the authors fall back upon examples from 

 the beaches and cliifs of the great lakes, although these are not 

 marine and lack the essential feature of a tidal flat. But it is 

 indeed remarkable how small is the proportion of sea-clifi" in the 

 coastline of the United States. 



The account of "The Origin and Descent of Eocks " in chap, vii 

 (pp. 375-462) covers a very wide range, and contains some original 

 features. Divided like the rest into numerous sections, subsections, 

 and titled paragraphs, it begins with an outline of the chemical 

 conceptions regarding rock-structure and molten magmas, and next 

 discusses the varied products derived from these magmas by cooling 

 under different conditions. In describing the "general names" — 

 greenstone, trap, basalt, etc. — that may be applied to igneous rocks, 

 it is stated that the name 'trap' "refers to the step-like arrange- 

 ment which the edges of the superimposed sheets of lava often 

 take" (p. 399), but this statement as it stands seems somewhat 

 misleading, as it might be taken to imply that the step -like 

 arrangement in question was originally present, instead of being, 

 in most cases, produced during subsequent denudation. 



The ' secondary ' (a somewhat ambiguous term for the ' sedi- 

 mentary ') rocks are then dealt with ; after which we are led to the 

 consideration of the ' internal alterations ' of rocks, especial 

 attention being given to ' carbonation and decarbonation,' to which 

 processes one of the authors, as is well known, ascribes wide- 

 reaching results. The processes as a whole are classed as 

 ' descensional ' and ' reascensional,' the former being those con- 

 cerned in the breaking down of rocks, and the latter those concerned 

 in their renovation. An outline is then given (in smaller type) of 

 the new system of rock-classification and nomenclature proposed by 

 American petrographers, and the chapter ends with a discussion of 

 ore-deposits. As the book is remarkably free from printers' errors, 

 we may call attention, in passing, to " the surface-water shave " 

 on p. 459. 



The chapter (viii, pp. 463-501) on "Structural (Geotectonic) 

 Geology " does not particularly impress us, and seems to lack 



