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, hke trap. If 

 this doctrine is correct when apphed to granite, I can see no reason wliy it may not be also 

 equally so when applied to hmestone. 



The annexed diagram is presented as 

 exhibiting phenomena of that kind and 

 chciracter, wliich 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 hyj^ersthene 

 rock at Long pond in the county of Es- 

 sex ; b, 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 foot of the mountain, which is about fifteen hundred feet above the pond or lake. This 

 shde is in the form represented in the cut ; and the limestone projects out from the naked rock 

 in the apex of the sUde, and is at least sixty feet wide. Its walls or sides are irregular, and 

 unhke the dj'kes 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 coimnon 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 locahty, 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 wliich 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 



