Modern Igneous Rocks and the Primary Formations. 113 
heat of ignition before ebullition will begin, and if the leaden 
waters of a deep ocean—for experiment as well as theory assures 
us of its great density—are for days in contact with the opened 
fires of submarine volcanoes, we can scarcely fix a limit to the 
temperature which they would necessarily receive. Why may 
they not be open for days and weeks? Why not hot springs in 
incessant action at the bottom of an ocean, as well as on our con- 
tinents; and in the early times of violent igneous action might 
they not have poured out floods in intense ignition, exceeding 
by no little in extent and temperature the bubbling fountains of 
the present day? And if, as is believed, the ocean had in early 
times a higher temperature than now, the effects supposed would 
be the more easily produced. 
We cannot doubt then, that here is heat sufficient to produce 
all the changes presented by the metamorphic rocks—heat enough 
to remould granite itself. In the words of Prof. Silliman, “we 
can see no reason for excluding water and other dissolving agents, 
acting with intense energy under vast pressure, and at the heat 
of even high ignition, from playing a very important part in erys- 
tallization ;” and he continues by remarking that the metamor- 
phic rocks of Lyell may thus have been crystallized. 
The facts observed in the vicinity of dykes are well accounted 
for on these principles. Numerous instances of altered rocks 
might be cited from foreign publications; but our own country 
furnishes them in great numbers and of unusual interest. 
Remarkable changes are described by Prof. H. D. Rogers, (Rep. 
N. J. p. 149,) as occurring at Rocky Hill, New Jersey, adjoining 
an extensive dyke of trap. The effects of heat in baking or 
hardening the intersected sandstone are distinct for a fourth of a 
mile from the dyke, beyond which the rock resumes its soft slaty 
structure and deep red color. Fifty feet from the trap, the sand- 
stone is filled with various crystalline matters, which render it very 
unequal in texture and hardness. About one hundred feet off, the 
rock is a compact reddish or purplish sandstone, somewhat argil- 
laceous, and is full of dark kernels or nodules of the size of a pea 
or less; one thin bed in the stratum contains small irregular cav- 
ities studded with crystals of tourmaline. The upper part of the 
same stratum is less altered in appearance but contains kernels of 
pure epidote, which continue to characterize the rock for a quarter 
of a mile, and at a quarry this distance off, besides the epidotic 
Vol. xiv, No. 1.—April-June, 1843. 15 
