PETROGRAPHIC GEOLOGY AND DESCRIPTIONS. 181 



Dialmse.] 



unbroken. These are principally chlorite flakes, magnetite powder, and occasionally 

 hematite and perhaps of biotite. 



In a section perpendicular to n t the extinction is 33 to 84, and on ,, is 57 to 

 61; on a section OTO it is 20, all of which agree well with M. Fouque (Bull. Societe 

 Mineralogie de France, vol. xvii, page 428) for htl>ra<1ortt<>. The specific gravity, 

 given above, is also a strong indication of labrndorite. In a section perpendicular to 

 an optic axis, extinction continues during a complete revolution. Foregoing (figure 

 6) is the appearance of a part of the thin section of No. 113, showing the outlines of 

 the grains, their cleavage, and their optical character in convergent light. A test by 

 the Boricky method gave microliths composed of lime and of soda. 



At/e. A transported block of Cabotian anorthosyte embraced in the Beaver Bay 

 diabase. 



Itt'iimrl,-. The stratigraphic and chronologic relations of this rock to the asso- 

 ciated rocks will be found discussed in the chapter on the structural geology; also, 

 in vol. iv, pages 299-302. N. H. w. 



No. 114. DIABASE (witholivine). 



Splitrock river. Occurs under the anorthosyte (No. 113) and to the east of it. 

 Ref. Annual Report, ix, page 30; Bulletin ii, page 103. 



Meg. An ordmary dark diabase, of medium grain, containing brownish blotches. 

 The feldspar is whitish, especially where weathered. 



Mic. The following is Dr. Wadsworth's description (Bulletin ii, page 103): 

 :< The structure of the section is ophitic and it is composed of divergent plaqio- 

 crystals cutting the irregular nu/jite masses. The section also contains much 

 H'fite and olin'i/r, which is altered along its edges and fissures to a yellowish 

 brown serpentine. The feldspars are clear, showing brilliant polarization, while the 

 augite is pale brown and contains much disseminated magnetite dust. The mag- 

 netite has, in places, a rectangular and oblique grating structure." 

 One section. 



Age. Cabotian. u. s. G. 



No. 115. DIABASE (witholivine). 



Splitrock point (Castle Danger). Massive dark rock, holding masses of feldspar rock (No. 113). 

 Ref. Annual Report, ix, page 30; Bulletin, ii, page 104. 

 Compare Nos. 116, 118, 524. 



Meg. Medium grained, resembling the rock composing Encampment island , but 

 less changed. 



Mic. The playioclase is twinned and embraced ophitically by the augite. It 

 shows a green chloritic stain, which runs in the cleavage and fissures. 



The augite has the usual two prismatic cleavages, and the parting of the 

 orthopinacoidal face, which is characteristic of dwllagc. Some of it is decayed, 

 giving rise to a chloritic substance and to magnetite. 



