288 Transactions. — Geology. 



5 . The theory also entirely fails to account for strata being elevated with- 

 out disturbance, imless we suppose such an amount of horizontal slipping of 

 one bed over another as is manifestly impossible. 



6. If, however, as appears to me certain, the rocks must crush and rise 

 tolei-ably uniformly, it is evident that the theory is quite inadequate to account 

 for mountains ; for, the conti-action being universal, and the sea occupying the 

 outer surface of the earth, the sea would rise ino7-e than the land, and the result 

 would be that after the contraction the sea would stand higher above the land 

 than it did before. In other words, the land would be said to have been 

 depressed instead of having been elevated. If, therefore, we consider the earth 

 when the crust was first formed, and it was surrounded by a universal ocean, 

 we see that no land could rise above the water from contraction, but that, on 

 the contrary, the ocean would gradually deepen. It was these considei-ations 

 that led me to suppose that the first deposits were of organic origin, and that 

 it was these deposits that first raised land above the watei\ 



7. Mr. Fisher assumes, without giving any reasons, that since the date of 

 the present surface features of the earth, a shell, 500 miles in thickness, has 

 contracted as much as rock would do in passing from a fused to a devitrified 

 state. But is this a reasonable assumption 1 I think not. It is certainly 

 q\iite as reasonable to suppose, with Sir W. Thomson, that it is 100 millions 

 of years since the crust of the earth cooled ; and if we suppose that the oldest 

 Laurentian rocks date from this period (which is the most favourable 

 supposition that can be made for Mr. Fisher), then the Cambrian period will 

 probably date about 50 millions of years ago ; and, taking the thickness of 

 formations as our guide, it is as reasonable a supposition as can be made that 

 of the other 50 millions of years 39 were occupied by the rest of the palaeozoic 

 era, 9 by the mesozoic era, and 2 by the cainozoic era. So that, if we suppose 

 the present features of the earth to have originated in the triassic period, it 

 follows that 11 millions of years is the oldest date than can be assigned to any 

 of them. This, by Fourrier's calculations of the rate of cooling of the earth — 

 allowing for the slight increase of radiation in former times — is only sufficient 

 to allow it to decrease 4° F. in temperatiu'e ; and if we suppose that the whole 

 of this heat was abstracted from the shell 500 miles in thickness underlying 

 the crust, its temperature would be reduced by only 12° F., which is not 

 nearly enough to give the amount of contraction supposed by Mr. Fisher. 



8. We can look at this question in another way. If the surface of the 

 earth has contracted, as Mr. Fisher supposes, one mile in a hundred since the 

 present surface features originated, and the circumference is now 24,856 

 miles, it must at the time supposed have been 25,104 miles in circumference, 

 and the radius, which is now 3,956 miles, must then have been 3,995 miles, 

 so that it must have shrunk 39 miles. This in 11 millions of years would be 



