Theories of the EarWs Physical Evolution. 325 



a different manner, and in a separate publication, arriving by a 

 different road at exactly the same conclusion with Captain Diitton. 

 It is, however, apparently to Mr. Fisher's paper " On the Inequalities 

 of the Earth's Surface " that Captain Dutton refers, and we would 

 make a slight correction in his allusion to it. Captain Dutton writes : 

 '' That gentleman, as if doubting the result of his own elaborate 

 computations, remarks that it is difficult to conceive any source, 

 other than contraction, of the intense corrugations which meet our 

 observation, and suggests that metamorphism and consolidation are 

 accompanied by a contraction of volume." We do not understand 

 Mr. Fisher as appealing to this cause to help to account for the 

 globe's contraction, but rather as making it an objection to 

 Babbage's theory of the elevation of sedimentary deposits through 

 their lower parts becoming heated. The doubts expressed were 

 not as to the results of hi& own computations, but rather as to 

 the truth of Sir William's supposition, upon which he had based 

 them, viz. that the earth is solid. 



To return to Captain Button's article. In seeking for the causes 

 which have produced the physical features of the earth's surface, 

 geologists require a supply of mechanical force : but that arising from 

 contraction from cooling is many times less than the quantity 

 required. But, if it be replied that the data on which this result is 

 obtained may still be erroneous, the most just course will be to 

 inquire whether, supposing the contractional theory be correct, it will 

 explain the facts to be accounted for. 



1. The origin of continents has been attributed to inequalities of 

 conductivity of different parts of the crust ; and the escape of heat, 

 and consequent contraction, has been supposed less beneath the land 

 than beneath the ocean. But continents, though they are geogra- 

 phically units, are in their geological relations highly complex 

 aggregates. Each portion of them has its own history, its own law 

 of development, its own stratigraphical series ; and still possesses its 

 structural peculiarities. And to be unmindful of such facts would 

 be to incur the risk of serious errors. 



The vertical movements have not been uniform. Certain areas 

 have repeatedly undergone submergence and emergence alternately ; 

 so that they must have been formerly regions of great contraction, 

 and have subsequently become regions of less. All those great 

 prominences, to which the term table-lands is usually applied, and 

 which form the most elevated portions of the earth, are covered with 

 heavy beds of marine strata of Mesozoic or Tertiary age — so far at 

 least as is now known. The Himalayan plateau reveals great bodies 

 of marine Tertiary beds, at an altitude of 16,000 feet above the level 

 of the sea. According to the hypothesis then, the rate of contraction 

 in this locality must have been, prior to the Eocene, greater than 

 the average ; but since the Eocene it must have been less. The 

 quantitative sufficiency of this cause to produce continents might 

 remain without question, if geology had furnished proof that it had 

 been acting continuously and cumulatively in one direction through- 

 out the whole period of evolution. As it is, whatever values be 



