MACKIE — ON THIS IJOTTOM-ROCKS. 
155 
causes ; so tliat this, as well as every other such isothermal line, would 
in any given vertical section present the form of an irregular undu- 
lating curve. 
Now wherever the deep oceans reposed, their water-masses would form 
natural conductors of the internal heat, and beneath them the lines 
of equal heat would recede more or less towards the centre. But 
wherever great quantities of sediment wei'e deposited, there the con- 
ducting power of the ocean-water would be prevented from action, 
and the isothermal lines below would ascend. Thus such deposits of 
sand and mud would be ex posed to the force of the subterranean heat ; 
and these new strata, if of limestone or other similarly heat-aifected 
substances, would expand ; and the result would be an elevation of 
territory. Thus, in North America, the great uplifted mass of the 
Alleghanies (Apalachiau Mountains) consists of Paleozoic sediments ; 
or, in other words, that uplift or elevation was of post- Carboniferous 
date. The Pyrenees, again, are of post-Cretaceous elevation ; the 
Andes of South America, the Alps in Europe, and the Himalayas of 
India are of post-Tertiary, or, more accurately, of post-Eocene date. 
If, on the other hand, the accumulated sediments subjected to the * 
action of the internal heat by the subterranean rise of the isothermal 
lines were of aluminous or other similarly heat-affected mineral mate- 
rial, a contraction might take place ; and, instead of an uplift, an 
extended depression, deepening the abyss of the ocean, might result ; 
and thus, by the various combinations, oppositions, and modifications 
of these expansive or contractile operations, new lines, or double, or 
parallel lines of elevation might be formed ; or the original lines of 
uplift and consequent weakness may either have been extended, like 
the successive extensions of the cracks of a starred pane of glass, by 
every thermal variation, or have been altogether broken down. 
By this rise of the range of the internal calorific influence up to, and 
its action upon, the inferior portions of the accumidated sediments, 
various kinds of granitoid and gneissic rock would have originated ; 
the granite being the lowermost portion fused, so to express it, under 
intense pressure of the superincumbent heap, in the presence of water, 
of a temperature perhaps equal to red-heat. As this granitized mass 
was forced up by its own expansion, it fissured the semi-crystalline 
and unchanged strata above it, dragging up, like a giant ou its shoulders, 
M 2 
