J. D. Dana — On displacement through intrusion. 375 



last, two methods here mentioned; that is, through deposition 

 from either an introduced solution or from oxidation of inside 

 pyrite (or other iron-bearing mineral). A specimen of this 

 pseudo-breccia, from Canaan, Conn., nearly three inches each 

 way, recently shown me by Mr. E. E. Cornish, of Norfolk, Ct., 

 consisted on one side of small angular blocks of the quartzyte, 

 irregularly displaced, and having the large interstices lined 

 and partly filled with limonite ; while on the opposite side, the 

 quartzyte was solid excepting a few fine rifts occupied by 

 limonite. The limonite in the specimen was so abundant that 

 it must have been derived from an outside source, and the mass 

 of quartzyte probably came from the gravel of a limonite deposit 

 or some place where limonite-making was going forward. Under 

 such a condition, the deposition of a coating of crystallized 

 quartz over the limonite might come from the silica which is 

 set free (and abundantly so) in the decomposition of the schist 

 adjoining the limonite-making locality. 



The interstices between the pieces of quartzyte are, as stated 

 above, only partly filled ; and hence open cavities are left. 

 This condition results because the separation, even though 

 wide, requires that the deposited mineral should cross the inter- 

 stitial space only at one or two points ; and when the limonite 

 deposit in the cavities is a smooth coating, or botryoidal, or 

 covered with drusy quartz, the cavity has become a small geode. 



The specimen figured below exemplifies a somewhat differ- 

 ent case of displacement by intrusion, coming under the 5th of 

 the above mentioned methods, which is essentially the same 

 with that of the pseudo-breccia in the method of applying the 



divellent force. It is a piece of well-characterized mica schist 

 of the muscovite variety, containing broken and displaced crys- 

 tals of black tourmaline. It was obtained on one of my Berk- 

 shire excursions of last summer from a quartzyte ridge up Eoar- 

 ing Brook, on the eastern border of the town of Lenox. 



The broken prisms of tourmaline are various in amount of 



