PETROGRAPHIC GEOLOGY AND DESCRIPTIONS. 177 



l>iul>ase.] 



No. 107. DIABASE (with olicinc, coarse). 



From the point opposite Encampment island. Compare No. 639. 

 Ref. Annual Report, ix, page 28; Bulletin ii, pages 112, 113. 



A rock similar to No. 106, but without the metalloidal reflections, and 

 in general better preserved; less spotted. 



Mic. Essentially identical with No. 106. The only noteworthy difference is 

 the greater amount of mm/net iti-, which is disseminated in the feldspars of No. 107- 

 In some cases these fine magnetite particles are arranged parallel with the twin 

 lamellae, and lie in a matrix of greenish substance which can be seen to be continuous 

 with the chlorite elsewhere very common. This chlorite and the magnetite have 

 accumulated, no doubt, simultaneously, and probably from the alteration of the 

 remnants of the magma. This only illustrates again the frequent association of 

 these two minerals as secondary results, and the migration of the iron element from 

 one grain to another. This chloritic substance in the interstices of the feldspars 

 can also be traced, sometimes continuously to the marginal parts of the feldspar, 

 where it gradually assumes the aspect and polarization of auyite, the magnetite 

 powder being its constant attendant. In most cases no continuous connection can 

 be seen between the chlorite-magnetite masses in the feldspar and the general 

 chloritic decomposition, and some of the included masses may be older inclusions or 

 impurities in the feldspar. They appear, however, to have the same origin as those 

 chloritic strings which are interposed between the cleavages. 



I 



One section. 



Ai/e. Cabotiau; probably the Beaver Bay diabase. N. H. w. 



No. 108. DIABASE (with olivine). 



PLATE I, FIGURE 2. 



From the high bluff at the mouth of Gooseberry river. 



Compare Nos. 517 and 518. 



Ref. Annual Report, ix, page 28. 



Medium grained, dark, with a mottled display of lighter and darker brown, 

 showing small grains or films of native copper. 



Mic. The section presents a fine illustration of the ophitic relation of the 

 iiuyite and/eWs/w, a phenomenon named "lustre-mottling" by Pumpelly. A single 

 augite crystal is cut by numerous microlites of plagioclase which have various orien- 

 tation. Throughout the area of this augite the opaque minerals are rare or wanting, 

 while they are abundant in the remainder of the slide. Therefore, even in non- 

 polarized light, the slide is spotted by light and dark portions, and when rotated 

 between crossed nicols the augite shows its size and colors independently. 



Oliriiic grains are small, and are apt to be entirely opaque or turned to a hema- 

 tite red by ferric oxide, thus resembling bowlingite. 



Two sections. 



Age. Cabotian; probably the Beaver Bay diabase. N. H. w. 



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