IGNEOUS ORIGIN OF LIMESTONE. 
39 
One of the strong arguments in proof of the igneous origin of granite was, that it shoots 
out into the adjacent rocks in veins, or cuts through them in the form of dyes, like trap. If 
this doctrine is correct when applied to granite, I can see no reason why it may not be also 
equally so when applied to limestone. 
The annexed diagram is presented as 
exhibiting phenomena of that kind and 
character, which I consider will place the 
two points under discussion in their true 
light and bearing : a, is a mass of coarse 
limestone, embraced in the hypersthene 
rock at Long pond in the county of Es¬ 
sex ; h, a mass of granite ; c, a bed of the 
magnetic oxide of iron ; and d, d, d, dykes 
of greenstone trap. The whole face of 
the rock has been completely laid bare by 
a slide, which is thirty or forty rods wide 
at the Toot of the mountain, which is about fifteen hundred feet above the pond or lake. This 
slide is in the form represented in the cut; and the limestone projects out from the naked rock 
in the apex of the slide, and is at least sixty feet wide. Its walls or sides are irregular, and 
unlike the dykes below. The most important fact to be noticed, is, that it comes up from the 
unstratified rock, and is not an accidental mass resting upon it, but is embraced in it as dis¬ 
tinctly as the dykes, the iron ore, or granite. 
This mass of limestone is filled with beautiful coccolite, varying in color from white, green¬ 
ish white, pale green, to deep green, and in fact it appears under every shade and variety of 
green, all of which have a fine lustre, which, imbedded as they are in white ground, or some¬ 
times a sky blue, forms one of the most showy minerals I have ever seen. Good crystals 
also of pyroxene occur here, of several modifications; together with large crystals of scapo- 
lite, phosphate of lime, and hornblende. A mineral much like idocrase is quite common in 
small brilliant crystals. 
The most important question is, the origin of the limestone. ' In relation to it, there are but 
two points, those already placed before the reader : the one, that it is a metamorphic rock, 
that is, a limestone originally sedimentary, and since changed by the adjacent rocks in a melt¬ 
ed state ; and the other, that it is an injected mass, analagous in this respect to granite, or a 
trap dyke, examples of which are furnished at this locality, and exhibited in the diagram. 
The first question then is. Is it metamorphic ? I should not probably trouble my readers 
with the discussion of this point; one which is so plain and so decisive, that it appears suffi¬ 
cient to state the case simply as it is, in order to establish the doctrine of igneous injection. 
But cases as plain and decisive as this, have been supposed by those of high standing as 
belonging to the,metamorphic class. 
That I may give fairly a full view of the subject, I shall here quote the opinions of several 
eminent geologists on phenomena of this character, though not on this particular locality. By 
