PETROGRAPHIC GEOLOGY AND DESCRIPTIONS. 445 



Diabase.] 



No. 601. DIABASE. ( Porphyritic. } 



From a dike about a mile north of Silver Islet landing. This roek gradually passes into No. 602, the 

 interval of transition being perhaps two feet, and the two run in the same direction as the Silver Islet dike. 

 The whole width is about forty-live feet, evenly divided between Nos. 601 and 602. 



Ref. Annual Report, x, page 56; A. E. Barlow, Ottawa Naturalist, vol. ix, pages 25-46, 1895 (Review in 

 the American Geologist, xvi, 1895, page 119). 



Meg. A medium-grained diabase, with coarse porphyritic crystals of a light- 

 colored feldspar scatteringly disseminated through it, the crystals in some cases 

 making about one-fourth of the entire rock. 



Mic. The rock is holocrystalline. The section shows only the groundmass. 

 The feldspar and the augite are ophitic in their relation to each other, the latter also 

 being sometimes distorted by dynamic movements. The rock shows the usual 

 characters of a somewhat weathered coarse diabase. 



One section. 



Age. Cabotian eruptive. 



Remark. Rock similar to this is seen frequently about the western environs of 

 Gunflint lake, in the form of sills and dikes in the Animikie of that region. Compare 

 Nos. 1314 and 2051. These coarse feldspars were named huronite by Dr. J. J. Bigsby, 

 but seem to be a saussuritized condition of the coarse labradorites of the rock, the 

 secondary grains being of high single refraction and probably of zoisite. N. H. w. 



No. 602. DIABASE. 



About a mile north of the "Landing" at Silver Islet; a dike. 

 Ref. Annual Report, x, page 57; Bulletin vi, plate XV. 



Meg. An ordinary diabase, of rather fine grain and quite heavy. 

 No section. 



Age. Cabotian(?) u. s. G. 



No. 603. DIABASE. 



Extremity of Pigeon point. 



Ref. Annual Report, ix, page 69; Annual Report, x, page 56. Compare Nos. 287, 291, 1843. 



Meg. A coarse-grained rock appearing more like a gabbro than a diabase. The 

 minerals are plagioclase, augite and olivine. Sometimes a few subporphyritic 

 feldspars are seen. 



Mi,-. The section shows a diabase of coarse grain composed of plagioclase, augite, 

 n/irine, iron ore and alteration products. The rock is a good representative of the 

 diabase (or gabbro) of Pigeon point described by Bayley (U. S. Geol. Survey, Bulletin 

 cix, pages 32-38), who gives analyses of the rock as a whole, of the feldspar and of the 

 augite. The feldspar is hihrndorite. The olivine is generally altered to a brownish 

 or greenish material (bowlingite?). The augite is in places also altered, the secondary 

 products being biotite, chlorite and quartz. The augite is, as a rule, later than the 



