PETROGRAPHIC GEOLOGY AND DESCRIPTIONS. 247 



Diabase. Sandstone.] 



associated with No. 187, which it overlies. It seems to embrace parts of No. 187 and then to take its place. The 

 corrugated surfaces are small, the wrinkles curving and being in various directions, sometimes like an inverted 

 basin. (The equivalent of No. 623.) 



Ref. Annual Report, ix, page 49. 



Mfg. A dark, medium- grained, ordinary diabase, which weathers softer, slippery 

 and smooth, more or less permeated with a whitish saponite (?) substance. 



Mir. Plates of augite embrace thefeldspars and the olivines, the latter frequently 

 altered to a brown bowlinyite. The section also embraces several large geodic areas 

 occupied by a greenish yellow, radiated, rather soft mineral, which is probably 

 closely related to the saponite (thalite) of the region. 



Age. Manitou. 



Remark. This rock is typical of a large series of dark traps (with much amyg- 

 daloid), which, beginning at or near the mouth of Baptism river, are in contrast with 

 reddish and laumontitic traps westward from that point. N. H. w. 



No. 189. DIABASE. 



" Caribou point, S. W. % sec. 10, T. 60-2. The rock of the point is represented by this number, and is of 

 the same horizon as No. 188. On the east side of the point this rock is basaltic radiatingly, and shows a thick- 

 ness of eight to twelve feet. The basaltic columns gradually give way to a bedded structure toward the north. 

 In some places it is fine-textured, especially near the top, and there shows the corrugations of the surface that 

 have been supposed to be old lava-crusts; but generally these are smoother than those seen at Temperance river. 

 This dips toward the lake at an angle of about 10 and lies on the next." 



Ref. Annual Report, ix, pages 49, 50. 



Meg. This is a dark brownish, fine-grained, diabasic rock, with some thalite 

 and calcite along seams and cracks. 



Mir. An ordinary, fine-grained diabase, composed of plagioclase laths, augite, 

 considerable iron ore (hematite and magnetite) and alteration products. 



One thick section. 



Age. Manitou. u. s. G. 



No. 190. SANDSTONE. 



"A brownish-red sandstone, or shale, so fragile as to fall to pieces by handling; within the bay inclosed by 

 Caribou point. This has a cross-lamination, and toward its junction with No. 189 is much less siliceous, and 

 more aluminous for a thickness of about twelve feet. Its dip causes it to disappear, and its fragile character to 

 become covered, within four rods of its first appearance, under No. 189. It reappears slightly about fifteen rods 

 within the bay, having the same dip. * * * It is plain that not much heat accompanied the overflow of No. 

 189, as it seems not to have affected No. 190, the transition being abrupt from one to the other." 



Ref. Annual Report, ix, page 50. 



Meg. A crumbling, poorly cemented, brownish-red sandstone of medium grain. 

 Some of the grains are rounded and some angular, and most of them are coated with 

 red iron oxide. The rock contains much calcite. The nature of all of the grains 

 of this rock is not easily determined, but they seem to be composed of material 

 derived immediately, without much transportation or abrasion, from basic amyg- 

 daloids. 



No section. 



Age. Potsdam. u. s. G. 



