ME. EOBEET MALLET ON VOLCANIC ENEEGY. 
163 
of the vast mass of comminuted material which has formed the assumed azoic and yet 
more or less stratified rocks, or of others of like character that may have preceded them. 
57. At length the crust became further indurated, and with its viscous bed beneath 
greatly thickened and convection cut off by it, as well as its coefficient of contraction 
diminished, arrived at that state in which it was thick enough to transmit tangential 
stresses within its own sheet. When the balance of contraction in a given time between 
the crust and nucleus beneath was such (the latter still in great part liquid, contracting 
fastest because of its large coefficient of contraction) that the crust began to transmit 
compressive tangential strains within its thickness, these were of great energy and acted 
through great ranges. And now the crust, thick and stiff enough to transmit these 
strains through great distances, began to corrugate and double up upon itself, and thus 
to elevate the greater and lesser mountain-chains, many of these overthrown and again 
elevated, whose united volume, could we obtain it, would be in some degree a measure of 
the total contraction of the spheroid, from the epoch of the crust having become thick 
enough to transmit powerful tangential thrusts down to a comparatively late geological 
period ; for whatever small changes in height may have occurred and are even now taking 
place (as in Sweden, &c.), no great elevations of mountain-ranges seem to have taken 
place in posttertiary or pleistocene periods. 
58. In this state of thickness of the crust of the cooling globe, on principles already 
alluded to in treating of the nature of elevatory forces, the great elevation produced by 
transmitted tangential thrusts must have been acccompanied by large induced or 
secondary orthogonal tensions , or extensions due to difference of thrust, and thus by 
great fissurings and by most of the great phenomena of faults and dykes and crystal- 
line-rock intrusions which we observe. 
59. Lastly, as refrigeration still proceeded and the crust became far thicker and more 
rigid, approaching in both respects the state in which it most probably now exists, 
began that balance and play of forces the effects of which are now recognized as 
volcanic, with their attendant phenomena of earthquake, thermal springs, See., and upon 
the precise mechanism of which we must now enter more largely. 
This, which we may call the period of volcanic regimen of our globe, in comparison 
with the brief span of human history, appears at the first glance one of uniformity. 
Yet it is one of decreasing energy, as has been the case with each of the epochs of 
refrigeration preceding it ; they could not have been otherwise if resulting from the 
thermal energies of a cooling globe. 
GO. We thus recognize four great stages of the operation of refrigeration, each less in 
energy than the preceding, but all due to the one all-pervading motive cause, loss of heat. 
1st. The formation and the deformation of a thin and flexible crust, and with it 
of the superficial parts of the viscous or liquid couche beneath, shaping out the 
land and sea boundaries. 
2nd. The splitting and breaking up of that crust and the more rapid (but 
irregular) cooling &c. produced by the first partial deposit of water upon the 
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