Dr. C. Ricketts—Changes in the Earth’s Crust. 169 
rivers, and what may be inferred from the contour of bays, which are 
the submerged continuation of valleys into which rivers flow, there 
must be sufficient, perhaps more than sufficient, power developed, not 
only to account for progressive subsidence of the Harth’s crust, but 
also to induce simultaneously, when circumstances are favourable, 
such lateral pressure, in the manner suggested, as would terminate in 
contortion and cleavage. However frequently such contortions may 
occur at the present time, opportunities of proving their existence 
must indeed be rare, for, formed beneath the surface of the water, if 
by any means they should become raised above the sea-level, the 
exposed surface of such easily disintegrated materials would be soon 
washed away by the waves. 
The contortions which occur in metamorphic rocks must, at least 
in a great measure, be dependent on other causes than those which 
have been considered. The abrupt bendings they have sometimes 
undergone ; the wavy wrinkled state into which they are at other 
times thrown, indicate that, to use an expression made to me by the 
Scotch chemist and mineralogist, Professor M. F. Heddle, M.D. of 
St. Andrews, “they must be due to some internal change.” Mr. T. 
F. Jameson, F.G.S., “supposes that the heat from the interior of the 
earth gradually approached the base of the sedimentary beds and, by 
heating, caused them to expand and thereby become wrinkled into 
huge folds, as a necessary consequence of a great mass of swollen 
matter having to find room in the space occupied by the same matter 
when in a cold and contracted state.1 Considered alone, this does 
not appear an altogether satisfactory explanation of the formation of 
such contortions as sometimes occur in metamorphic rocks. If the 
abrupt bendings alluded to are entirely the result of expansion from 
being subjected to excessive heat, it might be expected that in all 
cases foldings would result to a greater or less extent; or that, if so 
great expansion does take place, on the cooling and consequent con- 
traction of the mass, the resulting fissures should, in gneissic and 
granitic rocks, have their sides separate from each other to a greater 
extent than is the case; the average width of which does not appear 
to be greater than in unaltered strata. The shrinkage of basalt and 
lavas forms prisms, the joints of which are in close contact with each 
other, though the mass in which they exist has cooled from an 
absolutely molten state. Mr. Charles Babbage’ calculated, from the 
result of experiments by Mr. H, C. Bartlett, of the United States 
Engineers, that if a mass of granite, twenty-five miles in thickness, 
be heated to 1000°, expansion would take place to the extent of 
637 feet only; that is, there would be an extension of its bulk 
equivalent to about 34, of its size in a cold state. The results of 
other experiments, made by Mr. A. J. Adie, and by Mr. T. Mellard 
Reade,’ do not greatly differ from those of Mr. Bartlett. 
The expansion of rocks by increase of heat has by some been con- 
sidered to be the cause of elevation of the land. Doctor James 
1 Quart. Journ. Geol. Soe. vol. xxvii. p. 105. 
2 The Ninth Bridgewater Treatise, Appendix, p. 222. 
3 Origin of Mountains, p. 109. 
