UNDERGROUND PHENOMENA. 173 



Darwin, G. H. On the Influence of Geological Changes on the 



Earth's Axis of Rotation. Proc. E. Soc. vol. xxv. p. 328. See 



also Amer. Journ. ser. 3, vol. xiii. pp. 444-448. 



Considers the precession and nutations of an ellipsoid of revolution 



slowly changing its shape, the forms of continent and ocean-bed which 



by transportation would produce the maximum deflection of the axis, 



and the actual amount of rise and fall. A single large geological 



change may shift the pole 3°, and, the earth not being rigid, this effect 



may be cumulative. W. H. D. 



Desor, Prof. — . Sur les tremblements de terre et leurs causes. 

 [Earthquakes and their Causes.] Bull. Soc. Sci. Nat. Neuchdtel, 

 X. X. no. 3, pp. 342, 372. 



Dntton, C. E. Critical observations on Theories of the Earth's 

 Physical Evolution. Fenn. Monthly, Philadelphia^ May and June. 

 See also Geol. Mag. dec. ii. vol. iii. pp. 322-328, 370-376. 



Opposes Mallet's theory of the plication of strata and production of 

 volcanos by contraction of the interior mass from loss of heat, quoting 

 Sir W. Thomson's application of Eournier's conclusions to show that 

 the contraction since the globe solidified is insufficient to account for 

 the phenomena of disturbed strata. Points out that the character also 

 of the disturbances is against Mallet's theory, e. g. alternate submergence 

 and emergence, the occurrence of table-lands, and the neighbourhood 

 of little- disturbed regions to belts of great flexure. Plications occur 

 in regions of maximum deposit and at epochs during or immediately 

 following great deposition ; and in some regions there is a parallelism 

 between the axes of flexure and the axes of maximum sediment. Ad- 

 vances a theoiy that the elevations and depressions which occurred were 

 not relative but absolute. Regarding an uplifted area as the base of 

 an invert-ed cone, with the earth's centre for apex, shows that an uplift 

 involves an increase of volume, either by addition of matter or decrease 

 of density, while a subsidence implies the reverse. 



The subtraction and addition of matter from different areas by denu- 

 dation and deposition may account for a certain amount of rising and 

 sinking, on the supposition of the crust resting everywhere on a liquid 

 or plastic support ; but these will account only for as much movement 

 as would have kept the areas at their old levels. Another way in 

 which the additions of mass may occur is by the permeation of water. 

 This addition of water may not only increase the mass but affect the 

 density. It is probable that minerals in a state of hydro thermal solu- 

 tion are swollen and bulky. Hence an expansion would take place 

 when water at high temperatures finds access to rocks. This expansion 

 is made to account for upheavals ; and as soon as the density of the 

 underlying mass becomes less than that of the strata above, fractures of 

 the crust would ensue. Also where deposits were greatest masses 

 would sink in, protruding the colloid mass laterally and upwards 



