92 Observations on Pseudomorphism. 



Augite to Opal. — Dr. Blum suggests that this change is probably 

 effected by means of the sulphur vapors of the volcano decom- 

 posing the volcanic rock. The writer has seen siliceous incrus- 

 tations produced in this way at the sulphur beds of Kilauea, 

 Sandwich Islands, where the basaltic lavas are gradually crumbling 

 down, through this action, to a yellow earth. The sulphuric 

 acid removing the lime of the augite, forms sulphate of Ume, 

 which is foimd in snowy fibrous seams and incrustations. 



We do not attempt to offer explanations of all the several in- 

 stances of pseudomorphs. A more particular examination of the 

 various localities, the associate minerals and their situations in 

 the rocks, is necessary before this can be done. 



Tlie principal obstacle in the way of chemically investigating 

 and imitating these processes in nature, lies in these two facts; 

 1, that it is difficult by laboratory experiments, to appreciate the 

 effect of agents acting slowly for a long period of time, under 

 circumstances of temperature and electric forces beyond our cog- 

 nizance ; 2, we cannot know fully the exact condition and com- 

 position of waters intensely heated, underpressure, and rendered 

 by this means capable of dissolving many refractory minerals. 



In the preceding remarks, it has been our object simply to dis- 

 cuss the principal agencies that must have been in operation, in 

 order to prepare the way for a more complete elucidation of the 

 subject, by future developments. 



The importance of these discussions to geology, is not to be 

 measured by the length of the catalogue of pseudomorphs. The 

 same process that has altered a {e''N crystals to quartz, has distri- 

 buted silex to fossils without number, scattered through rocks of 

 all ages. The same causes that have originated the steatitic 

 scapolites, occasionally picked out of the rocks, have given mag- 

 nesia to whole rock formations, and altered throughout their phys- 

 ical and chemical characters. If it be true that the crystals of 

 serpentine are pseudomorphous crystals, altered from chrysolite, it 

 is true also, as Breiihaupt has suggested, that the beds of serpen- 

 tine containing them, are likewise altered, although often cover- 

 ing square leagues in extent, and common in most primary re- 

 gions. The beds of steatite, the still more extensive talcose for- 

 mations, contain every where evidence of the same agents. The 

 deposits of the so-called Rensselaerite, in northern New York, 

 are other examples of the widely extended influence of the 

 pseudomorphic agencies. 



