118 Mr. Dana on the Analogies between the 
of the most extensive volcanic action in the world, and while 
below the ocean—which was the case, as the tertiary rocks of the 
summit seemed to indicate, till the tertiary period had somewhat 
advanced—every eruption produced a heated sea around and 
through them, which hardened the porphyry conglomerates and 
sandrocks, till they were almost porphyry again. And it may » 
be that the feldspar crystals imbedded in, the metamorphic rock, 
instead of being the refuse from porphyry eruptions or por 
degradations, were crystallized by the metamorphic heat. 
Having discussed the action of heated waters on the various 
secondary rocks, and shown that the changes the structure of 
these rocks has undergone is attributable to this cause, we pass 
by a natural transition to granitic formations, and would endeavor 
to prove that no new cause is required for similar effects in them. 
With the knowledge of a power so efficient and so capable, so 
essentially connected with submarine eruptions and so frequent 
in its action, we need no other theory to account for any meta- 
morphic changes. ‘The same that holds good for red sandstone 
and will account for crystallizations of epidote and tourmaline, 
the same that accounts for metamorphic porphyry, is as good for 
metamorphic gneiss or granite. The structure of granitic rocks, 
their uniform compactness without an air-cell the world over— 
has often been urged as proof that they were formed under some- 
thing more than atmospheric pressure. Beneath this pressure, 
whatever it may have been, we are safe in saying that the ocean 
was raised to a temperature far beyond that producing the erys 
tallizations in the red sandstone. Mica and feldspar were also 
erystallized, and the sedimentary deposit was changed ee? to 
granite or to some of the associated rocks. 
To explain this subject more completely, I will trace out some 
of the analogies that exist between the ancient granitic pei: 
and the more modern igneous rocks and deposits. “ 
A sedimentary basaltic sandrock or conglomerate is often:s0 50 
associated with basalt,.as to make it obvious that they were 
formed together—the Gastar arising from the sand or fragments 
carried off from the ejected basalt by the action of the water oD 
the heated rock. An instance of this kind in Illawarra, New 
h Wales, is too plain to be mistaken. The basalt occurs in 
layers alternating with sandstone, the sandstone having beet 
formed in the interval between-different basaltic eruptions. “The 
