PETROGRAPHIC GEOLOGY AND DESCRIPTIONS. 257 



Laumontite. Breccia. Diabase.] 



No. 203A. LAUMONTITE. 



From a vein in No. 203. The specimen is in the form of crumbled powder, rather coarse, of a light-pink 

 color. 



Ref. Annual Report, ix, page 53. j^ jj. W. 



No. 204. BRECCIA. 



Nos. 204, 205 and 206 are transition rocks, in the order numbered, between Nos. 202 and 203. 

 Ref. Annual Report, ix, page 53. 



Meg. A red, fine-grained, shaly rock, containing much laumontite. The hand 

 sample contains a few apparent fragments of a rock very similar to the rest of the 

 hand sample, but more compact, finer grained and not containing laumontite. 



No section. 



Age. Cabotian. u. s. G. 



No. 205. DIABASE. ( Contacting. ) 



A supposed transition rock between Nos. 202 and 203, as stated above. 

 Ref. Annual Report, ix, page 53. 



Meg. Compact, fine-grained, brown or gray, with some reddish brown small 

 crystalline angular areas, as if of a rusted feldspar. 



Mir. There are remaining some feldspar forms, but they are filled with 

 impurities. They can sometimes be distinguished as twinned triclinic crystals. 

 Narrow, slender, greenish crystals, with feeble absorption, cut across the rock. 

 These extinguish sometimes at a large angle, .approximating 26 with the nicols, 



* 



and have a conspicupus cleavage parallel with their elongation; also an irregular, 

 coarse fracturing, simulating a cleavage, which is oblique to the other. At other times 

 they extinguish nearly parallel to their elongation, but in this case the cleavage is not 

 evident, and the section is obviously not parallel to the edge m m. This mineral 

 also has a high refractive index. It is either hornblende or angite, and the last 

 mentioned character points strongly to augite. The most of the rock is not distinctly 

 crystalline, but poikilitic quartz areas spread through it. 



One section. 



Age. Cabotian. N. H. w. 



No. 206. DIABASE. 







See under No. 204. 



Ref. Annual Report, ix, page 53. 



Mi'</. A fine-grained, dark, diabasic rock. It contains a few small areas, appar- 

 ently pseudamygdaloidal, of quartz; also of calcite, and along a seam some soft 

 saponite-like material. The hand specimen also contains fragments, not always 

 sharply separated from the rest of the rock, of a very fine-grained, brownish rock. 



Mic. The section shows a fine-grained diabase, with plagioclase laths, augite, 

 magnetite, henidtife and large amounts of confused, dirty, greenish to brownish, 



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