Cwpf. F. W. Hutton — On the Formation of Mountains. 25 



was understated, so tnucli the more would my example tell against 

 myself. The rocks below the Cretaceous formation were not taken 

 into consideration, because they were the old surface, and had nothing 

 to do with raising the temperature. Neither did I ever regard the 

 Wealden area as an isolated dome-shaped elevation ; but the other 

 elevated areas have, by the Deposition theory, nothing to do with the 

 amount of elevation of the Weald. 



With reference to the latter part of the paragraph, it is, I believe, 

 uncertain, whether the Tertiary rocks ever extended over the Chalk 

 or not ; at any rate the fresh- water beds, as well as the vegetable 

 remains of the London Clay, show that land was then in the 

 neighbourhood, which land must have been elevated since the 

 deposition of the Chalk on the bottom of a deep sea. The depression 

 succeeding the Woolwich beds no doubt took place after the dome of 

 the Weald was formed ; but I must leave these details to be worked 

 out by those geologists who have an intimate local knowledge of the 

 district. 



Hitherto I have confined myself to urging the claims of the 

 Deposition theory; but as Mr. Fisher says that he has "not had the 

 good fortime to hear of the many arguments which have been urged 

 against" the theory that he advocates, I will briefly state the reasons 

 that have led me to reject the Contraction theory as giving a sufficient 

 explanation of the formation of mountains. I do so with the less 

 reluctance because nearly all opposing theories in Natural Science 

 must ultimately be weighed by the balance of probabilities; and it is 

 therefore just as important to argue against a theory as to argue in 

 favour of it. 



My reasons for rejecting the Contraction theory are — 



1. Contraction of the globe would not produce any tangential 

 pressures except in solid rock, so that the lateral compression must 

 be confined to the crust. Consequently the more rapid contraction 

 of the lower beds could only cause the upper beds to rise into 

 anticlinals by one solid portion slipping horizontally over another 

 solid portion. This appears to me to be mechanically impossible, 

 because the resistance to shearing would be far greater than the 

 resistance to crushing. Neither do we find in nature any horizontal 

 faults, which ought, if the Contraction theory be true, to be numerous 

 and on an enormously large scale. For instance, in the example 

 given by Mr. Fisher (Trans. Cam. PhH., 1869, p. 15, fig. 3), the 

 central part must have been horizontally faulted over the lower con- 

 tracting beds for half a mile. In this way utter confusion would 

 reign in stratigraphical geology ; Paleeozoic rocks would have slid 

 for miles over Mesozoic rocks. Granites over Sedimentary rocks, etc. 

 It is quite certain that nothing of the kind has taken place in any 

 portion of the earth's crust that has been examined. Nevertheless 

 this view is accepted as probable by Prof. Shaler, when advocating 

 the Contraction theory (Proc. Bost. Nat. Hist., 1866, and Geol. Mag., 

 Vol. Y. p. 511), and Mr. Fisher appears to see no difficulty in the 

 thrust being extended through 50 miles of rock (1. c. p. 15, fig. 3) 

 when advocating the Contraction theory, although, when criticizing 



