122 Mr. Dana on the Analogies between the 
By the application of these views we may possibly discover 
hereafter, the cause of the peculiar distribution of specular and 
magnetic iron in New York, and of the hydrous oxyd of iron, 
or hematite, in New England, and why chromic iron is so com- 
mon a serpentine mineral, while it is not found at all in other 
rocks. Indeed may we not now explain the occurrence of this 
chromic iron? Is it not for the reason that the green oxyd of 
chromium will not stand the dry fire, and cannot be formed, there- 
fore, except through the agency of heated waters? 
There is much reason, therefore, to believe that serpentine is — 
a metamorphic rock, altered by heated waters containing magne- 
sia and silica in solution. ‘This rock has been compared to cer- 
tain greenstones. ‘Trap and the allied rocks have been shown 
by late analyses to consist of feldspar, augite or hornblende, and 
sometimes chrysolite and iron, together with one or more zeolites. 
The same hydrous minerals that fill amygdaloidal cavities, should 
be expected to fill all the pores or interstices in the rock itself, 
and this is what is now proved by analysis. The deposition of 
chlorite in the same cavities, shows that this mineral may also be 
disseminated through trap or basalt, and also that the basalt may 
possibly be more or less altered, and rendered more magnesian 
than is usual with this rock; and in this way we may conceive 
how either of these rocks should assume a serpentine character. 
I met with dykes of greenstone in Chili which could scarcely 
be distinguished from some serpentine. 
It follows necessarily from these views that the granular lime- 
stone associated with serpentine must also be an altered or meta- 
morphic rock. Ido not mean that it was ever a compact lime- 
stone, like those of secondary formations; it may have been so 
or it may have been an aggregate arising from the wear or degra- 
dation of the igneous limestones. In either case it has been 
changed in its structure or recrystallized. Among the minerals 
in these rocks, the few hydrous species, are probably of aqueous 
origin. The rest may be either igneous or aqueous; more facts 
must be known before they can be distinguished. 
There is evidence that some limestones after crystallization 
and the formation of some or all the imbedded minerals, were sub- 
jected anew to heat. ‘The fused quartz, and rounded apatites of 
St. Lawrence Co., N. Y., have been so explained by Prof. Em- 
mons, and I would only suggest as an addition to Prof. Emmons’s 
