156 
ME. EOBEET MALLET ON VOLCANIC ENEEG-Y, 
Fig. 1. 
vertical. Thus tlie deficiency in density more recently found, or with good grounds 
suspected, as occurring beneath great mountain-masses receives its solution, whilst a 
greater density there would be the necessary result of direct vertical pressure. 
29. Thus it is evident that the tangential, or nearly tangential, and opposing pressures 
t and t', resolved into the vertical e, by 
which the upraised mountain-mass is lifted, 
tend to reduce the density, if not to leave 
actual hollows, about h, below the level of 
the intersection of those three lines of force 
and above that at which the tangential 
forces are completely horizontal ; but that 
a directly vertical lift, as by d continued on 
by e to the summit, must tend to produce 
increased density about h. 
30. The intense plications and foldings over of strata and absolute overturn of whole 
mountain-masses, seen in all great regions of elevation, the tremendous bending, foldings 
over, and smashing up of beds, such as M. Burat’s sections of the Coal-formations of 
Central France or those of D'Halloi and Yon Dechen of the formations of Belgium and 
of Westphalia, become thus accountable for, as are, indeed, all the salient phenomena 
presented by the surface and sections of our earth’s crust, to follow out which in detail 
here is impossible. 
31. One or two important results which follow from Prevost’s grand hypothesis, that 
all forces of elevation, in a word, the only known vertical lifting agent (volcanic vents 
excluded), are resolved or transformed tangential forces of compression due to contraction, 
and acting in antagonism at various but no very great depths beneath our globe’s present 
surface, which as yet have attracted no attention, should be at least alluded to. 
32. These tangential forces of compression, acting slowly, not at all points uniformly 
or alike at all times, and on the whole (as the globe cooled) with a diminishing intensity, 
act simultaneously, though unequally, over great areas of sectional surface of the earth’s 
crust. Relatively to the tremendous crushing-power of the tangential forces themselves 
and to the long continuance of their action, the materials on which they act must be 
viewed as more or less plastic. 
33. It follows that if by resolved tangential pressures acting against each other in one 
direction, or in parallel directions along lines or in planes, elevations are produced, the 
compressions in these directions must be accompanied by extensions in the orthogonal 
directions, by difference in resistance to pressure producing tensions. 
34. Hence, by the final resolution of tangential compressions, surfac e-fissures may 
follow from these orthogonal tensions, so that generally the compressions shall give 
rise to crumplings up and crushing together of strata, to elevation, and to fissuring; in 
which last the phenomena may simulate the effects of direct elevatory forces, according 
with Hopkins’s hypothesis. And this is the reason why the actual directions of observed 
