348 Mr. C. Chree on some Applications of 



the " temptation is strong to waste upon it a collateral glance " 

 (/. c. p. 259). Accordingly he crushes Sir W. Thomson's 

 argument* from the tides by the remark — " That a siliceous 

 crust of 20 miles average thickness, and an overlying aqueous 

 ocean of three miles average depth, should have (as required 

 by the argument) so equal a coefficient of mobility, that sea 

 and land could thus together l rise and fall,' might well be 

 pronounced incredible" (/. c. p. 260). 



He regards Sir W. Thomson as very seriously damaging 

 his own argument by the admission that tides comparable in 

 magnitude with those observed would occur even in a solid 

 earth of steel. It does not seem to have occurred to him that 

 the existence of a difference between the motions of the land 

 and water may constitute an argument for solidity f. 



Mr. Taylor admits one difficulty in his theory, viz. the 

 nature and local characteristics of the plications actually 

 observed ; and remarks: — " While the force at the command of 

 the rotating planet is abundantly sufficient . . . evidently some 

 supplementary considerations are requisite to give the observed 

 direction to this force," ... " The mere mechanical difficulty, 

 however, of transmitting stresses through comparatively un- 

 disturbed areas of hundreds of miles of a flexible, friable, and 

 practically plastic crust — with a large coefficient of viscous 

 friction beneath — is not so formidable as might at first appear. 

 It must be borne in mind that the pressures derived from an 

 action so slow as from century to century to be scarcely 

 sensible, are of an order of very great intensity, but of very 

 small quantity" (I. c. p. 265). Mr. Taylor also infers from 

 " various considerations " that " in all ages mountain building- 

 has been at a maximum ; that is, the uplifted heights have 

 been the greatest which the average thickness of the crust at 

 the time was capable of supporting ; so that the former has 

 been a constant function of the latter, the ratio being probably 

 not far from one-fifth" (l. c. p. 265). Mr. Taylor does not 

 state that this law of the uplifted heights is true of all lands 

 as well as of all time, but the possibility that such may be the 

 case is rather alarming. He enters in fact into no unnecessary 

 details as to how he reached his conclusions, so that all one 

 can say is that measured by his own standard he is certainly 

 not inferior in physical insight even to Mr. Herbert Spencer. 

 Perhaps when he comes to deal with the " supplementary 

 considerations " he may supply sufficient data for the mathe- 

 matician to follow him. 



Professor Prestwich, in his i Geology, 5 vol. ii., regards the 



* Natural Philosophy, vol. i. part ii. § 833. 

 t See his remarks, /. c. p. 260 and footnote. 



