90 Observations on Pseudomorphism. 



We cannot doubt, especially when we consider the vast pres- 

 sure of an ocean, that these waters, besides overlying, fill up all 

 open spaces or caverns between the layers of submerged rocks, 

 and probably the whole substratum of the ocean, when not loo 

 compact, is throughout permeated by them. Submarine erup- 

 tions opening to the fires below and sometimes ejecting lavas, 

 would distribute heat around and thus give the waters increased 

 power in their action upon rocks. This cause therefore is suffi- 

 cient in its energy, and sufficiently extended in its influence. It 

 must have been iti action ever since the earth had an ocean and 

 internal fires ; for it is a necessary effect of all submarine volcanic 

 action. Wherever a trap dyke is to be found on the globe in a 

 vein of porphyry, there have been heated waters, permeating and 

 superincumbent, and under the pressure of an ocean intensely 

 heated. 



Additional magnesia would be furnished these waters by the 

 various augitic rocks, among which the traps are included; also 

 by dolomites.* 



The action of heated waters is often indicated in the regions 

 of these pseudomorphs, by the rounded angles or pitted surfaces 

 of otherwise unaltered crystals. 



Other evidence that heated water has been the agent, is found 

 in the frequent change of quartz to steatite. Hot magnesian 

 waters alone, could have effected the slow solution of the silica 

 and the introduction of magnesia, that constitute the change 

 here indicated. Hot vapors it is true would equally dissolve sil- 

 ica, but they would not afford the necessary magnesia ; and more- 

 over, exposure to such vapors would have destroyed the form of 

 the crystal. 



This view is farther corroborated by the occurrence of sili- 

 ceous pseudomorphs along with those of steatite. The steatitic 

 spinels, also, of the same localities afford other proof, as the change 

 in these crystals has consisted in a substitution of silica for alu- 

 mina, thus making a silicate of magnesia out of what was be- 

 fore an aluminate of magnesia. — a change that requires water and 

 heat for the solution of the silica, and heat no less for effecting 

 the transfer of elements. 



* The interesting analyses of B. Silliman, Jr. have shown that the ocean's wa- 

 ters through animal agency, (the growth of corals,) have afforded a great part of 

 the magnesia that is contained in dolomites ; (see this Journal, Vol. xlvii, p. 135.) 



