456 J. D. Dana on Dolomite Pseudomorphs 
 and-magnesia (dolomite), and solutions containing iron silicates, 
were together, and in all probability at a very high temperature. 
ence we may reasonably conclude that under such cireum- 
stances the magnetite was deposited. 
D. PSEUDOMORPHS CONSISTING OF PYRRHOTITE, OR THE SULPHIDE oF Iron FS. 
15. Pyrrhotite Pseudomorphs after Serpentine. 
The thin plates in the pseudomorphs, No. 11 (p. 450), some- 
. . . 
times consist, in part of the specimen, of pyrrhotite instead of 
proves it to have been one of the later products. The altera- 
tion of the green plates, and not of the intervening white ser- 
pentine, may have been owing to the presence in the plates 
still of some iron. 
E. PSEUDOMORPHS CONSISTING OF DOLOMITE. 
16. Dolomite Pseudomorphs after Chondrodite. 
Implanted crystals of chondrodite occur sometimes with an 
deposition of dolomite took place concurrently with the re- 
moval of the chondrodite. The crystals that have a coat of 
dolomite, and those that are all dolomite, have the same size, 
which proves that the deposition of the crust was attended with 
a removal of chondrodite, and probably an equal bulk of it. 
The dolomite was chemically examined and proved to be this 
species by Professor Allen. It is a concretionary kind, such as 
is found as a crust over the serpentine of some specimens. 
Crystals of chondrodite coated with magnetite (No. 14) occur 
on the same specimens with these dolomite pseudomorphs after 
chondrodite ; and the corroding and removal of the chondrodite 
was probably effected in the case of both by the same chemical 
4.—ConcLUSIONS AND RECAPITULATION. 
» tions by which the changes were brought about. 
