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eludes that " the large discrepancy (pointed out in chap, vi.) shows 

 that the hypothesis, that the inequalities of the surface have been 

 caused by the cooling and consequent contraction of the earth re- 

 garded as a solid globe, is untenable." Hence the author thinks 

 we are shut up to one or both of the following alternatives : "either 

 the inequalities of the surface are not altogether, or even chiefly, 

 due to lateral compression ; or there has been some other cause in- 

 volved in producing the inequalities of the crust other than the 

 contraction of a solid globe through mere cooling The shift- 

 ing of the crust towards a mountain-range, which is testified by the 

 corrugation of the rocks of which it is formed, requires a more or 

 less fluid substratum to admit of it. The sinking of areas such as 

 deltas, and other regions of deposition, demand a like arrange- 

 ment; and, in short, it appears that the crust, in the form in 

 which it exists, must be in a condition of approximate hydrostatical 

 equilibrium, such that any considerable addition of land will cause 

 any region to sink, or any considerable amount denuded off an area 

 will cause it to rise." In Chapter VIII. the hypothesis of a fluid 

 substratum is discussed in connexion with Mr. Hannay's recent 

 experiments ; in Chapter IX. the supposition of an inflexible crust is 

 dismissed ; and in Chapter X. the analogy between the condition of 

 the crust and the case of a broken-up area of ice, refrozen and float- 

 ing upon water, is worked out to the conclusion that " the crust is 

 certainly less than 30 miles thick." In Chapter XII. we get the 

 result, " The crust of the earth at a place near the sea-level is about 

 25 miles thick ; beneath the central parts of the ocean it is about 

 20 miles thick, or perhaps less, and that it is more dense in those 

 regions " *. The contraction is next calculated on the two suppo- 

 sitions that oceans are due (1) to compression, (2) to a denser 

 crust ; and the outcome of the discussion is that the ocean-basins 

 are thought to be due to a greater density and general depression 

 of the suboceanic crust. Then it is shown that the oblateness 

 may have been altered by changes in the rotational velocity ; but 

 Mr. Fisher thinks there is no indication in the arrangement of 

 mountain-chains of their having been connected with such a mode 

 of action. In Chapters XV. to XXI. the alternative hypothesis is 

 examined, viz. that the causes of compression are situated within 

 the crust itself. We content ourselves with giving the titles of 

 these Chapters: — Compression and Volcanic Action (Prof. Nor- 

 denskiold's theory and the views of American geologists are 

 amongst the matters treated of in this chapter) ; on Faulting ; 

 Geological Movements explained; Mr. Mallet's Theory of Volcanic 

 Energy (opposed to Mr. Fisher's results) ; the Volcano in eruption 

 (discussion of theories of Scrope, Dalton, Mallet, and Eichthof en) ; 

 Sequence of Volcanic Rocks ; and, lastly, Geographical Distribution 

 of Volcanos. 



Mr. Fisher closes with reminding his readers that his work 

 " deals with a great number of questions, each in a very superficial 



* The densities given are — suboceanic 2-955, continental 2-68, 



