Dr. O. Ricketts—Changes in the Earth's Crust. 117 
currence of earthquakes to the formation of fissures described as 
“falling” or “slipping” ; the blow thus occasioned being felt as an 
earthquake. Fissures and displacements likewise occur as the effect 
of the shock, in unconsolidated strata or in the banks of rivers; 
this latter was especially evident in that of Cachar, Hast Indies, in 
1869; but instances have been recorded in which an extent of land 
has at the time of the shock separated and changed its level under 
such circumstances as are indicative of the formation of these faults 
having originated and caused the earthquake. Several have been 
described by Lyell,! and also by others. 
On two occasions systematic attempts have been unsuccessfully 
made (by Mr. Robert Mallet after the Neapolitan earthquake of 
1857 ;? and by Dr. Oldham with respect to that of Cachar in 1869 ; *) 
to discover the exact site, the cause of displacements, or the changes 
which originated the shocks, by tracing back the secondary effects 
to their source. Though in each case the near neighbourhood whence 
the shock originated was determined, the exact cause was not 
discovered. 
Contortions of strata, even those of great extent, have very 
generally been attributed to secular cooling of the earth, consequent 
on its crust being compressed into a less space as it followed the 
cooling and therefore sinking nucleus. But if subsidence has 
occurred from such a cause, how is it that, with an increasing loss 
of caloric, the areas supposed to have been depressed in this manner 
have been again raised, it may be to a greater height than that 
which they previously occupied? Sir Charles Lyell remarked that 
“the wide extent in North America, and in parts of Russia, of 
Carboniferous, Devonian, and Silurian strata, which, although 
upraised above the sea, continue almost as level as when the beds 
were first thrown down beneath the waters, clearly demonstrates 
the limitation of the agency, to which great foldings and contortions 
of stratified rocks have been due, to very confined spaces in each 
epoch ;’* but as these localities are to a great extent situated in 
regions of excessive cold, in some so intense that the ground is 
frozen to the depth of many hundred feet, it, I think, likewise 
follows that, if loss of heat can induce flexures, it must be, as in 
these instances, to a very limited extent. 
Mr. T. Mellard Reade, F.G.S., considers “there is a fallacy in 
the reasoning which attributes the corrugation of the earth’s surface 
to the contraction of the nucleus” and ‘has arrived at the 
conviction that the cooling of our earth has not extended to such a 
depth that we need consider the internal contraction as a geological 
cause.” ® 
The Rev. Osmond Fisher, F.G.S8., goes farther; he has calculated 
1 Principles of Geology, vol. ii. chap. xxviii.- xxx. 
2 Report of the Royal Society of London to investigate the great Neapolitan 
earthquake of 1857. 
3 Memoirs of Geol. Survey of India; vol. xix.; also Quart. Journ. Geol. Soc. 
vol. xxviii. p. 255. 
* Quart. Journ. Geol. Soc. vol, vi. p. xlii. 
5 Origin of Mountain Ranges, p. 125. 
