PETROGRAPHIC GEOLOGY AND DESCRIPTIONS. 175 



Quartz-laumontite. Diabase.] 



thick section it is almost impossible to determine its extinction, since it is governed 

 in its color and its illumination by its host. When, however, the fibres make up 

 the whole thickness of the slide the elongation is seen to be negative. Extinction is 

 apparently about 5 from parallelism with elongation, which indicates, with other 

 characters mentioned, that this zeolite is mesolite (Min. des Roches, pages 298, 314). 

 The appearance of being sometimes positive and sometimes negative is not due to 

 the intermingling of mesolite fibres which are positive, but this is a characteristic 

 quality of mesolite, making it, in that respect, resemble thomsonite,* from which, 



however, it differs markedly in its low double refraction. After the formation of 

 the zeolite the loose mesh was filled by infiltrating silica. 



One section. 



Age. Cabotian. N. H. \v. 



No. 104. QUARTX-LAUMONTITE. (,S'r<//c.v. ; 



From the layer of diabase which lies near the lake level below the buttresses of amygdaloid, at the great 

 natural bridge at the east side of Burlington bay. 

 Ref. Annual Report, ix, page 27. 



Meg. Compact, flesh-red, about a quarter of an inch thick, lining joints in the 

 trap. Consists apparently of a dense intergrowth, in a granular manner, of laumon- 

 tite and quartz. The scales examined consist of fragile, nearly white laumontite 

 on one side, and of siliceous, red, granular, hard substance on the other, the two 

 portions fading into each other. 



No section. 



Aye. Cabotian. N. H. vv. 



No. 105. DIABASE (with 



Point on the coast, sec. 22, T. 53-10, just east of Silver creek. 

 Ref. Annual Report, ix, page 28; Annual Report, x, page 64. 



Fine grained, brown, scarcely porphyritic. 

 Mir. Feldspar appears in two epochs of generation, the earlier crystals being 

 quite rare, and having a central area charged with impurities. The smaller crystals, 

 resulting from the final consolidation, have independent orientation amongst the 

 (tiiyiti; crystals, the latter being almost always reddened by ferric oxide. Olivine 

 forms remain, but they are converted to a greenish, almost isotropic, substance. 

 One section. 



Ayr. Cabotian. N. H. w. 



No. 106. DIABASE (with olivine, coarse). 



The rock of which Encampment island is composed. Compare. Nos. 128 and (538. Carries masses of 

 anorthosyte. 



Ref. Annual Report, ix, page 28; Annual Report, x, page 64; Bulletin, ii, page 113. 



* Miniraloyie de France, vol. li, p. 278. 



