Modern Igneous Rocks and the Primary Formations. 111 
actually exist, for there is little satisfaction and little profit in 
arriving at conclusions that are false. But before my remarks 
are closed, I shall hope that some of these doubts may be removed. 
I proceed next to the third point before us—that the heat pro- 
ducing metamorphic changes, has been applied through the wa- 
ters heated by the eruption itself. It isa little surprising that 
this cause of change in rocks should have been so generally dis- 
regarded or rejected, by the geologists of the day. It bears a 
slight tinge of Wernerism, and this may be its repulsive feature. 
One of our own most distinguished geologists, Prof. Silliman, 
first brought forward its claims, and urged them with conclusive 
arguments in the geological discourse appended to the American 
edition of Bakewell’s Geology. Prof. Silliman has drawn his ar- 
guments from what is believed to have been the condition of the 
globe while the granite rocks were forming. I shall pursue far- 
ther the same mode of reasoning, and deduce other evidences 
from the analogies which may be found in regions of acknowl- 
edged igneous action. 
Mr. Lyell in his metamorphic theory, treating of formations 
remote in origin from our own era and the present order of things, 
has necessarily indulged more freely in hypothesis than is to be 
found elsewhere in his geological writings. If any well-ascer- 
tained facts could be pointed to as a basis for his hypothesis, it 
might be received with less caution than it now demands. But 
in truth there are no changes Ixnown to be in progress of the char- 
acter supposed, and although possible, analogies do not authorize 
us to consider them by any means probable. How is it in active 
volcanoes? Lavas may be heated to a red heat within a yard of 
the surface and still be so cool above, that the bare foot may walk 
upon them. ‘'T'o produce metamorphic changes in a deposit a 
hundred feet thick, the whole must consequently be in a state of 
fusion, or the upper crust will not be done through. We all know 
how small a thickness of fire-brick it requires to confine the heat 
of the hottest furnace. And if, as we believe, the heat attending 
granite eruptions far exceeded common volcanic temperature, our 
conclusions are still the same. The excessive heat in a furnace 
first fuses the inner surface, or the inner bricks, and thus by melt- 
ing its way along, slowly commences a change on the outer row, 
and. three inches only may intervene, between the heat of fusion 
and the temperature which does not pain the hand. 
