PETROGRAPHIC GEOLOGY AND DESCRIPTIONS. 459 



Diabase. Conglomerate.] 



Remark. This thin section, necessarily from one of the more firm parts of this 

 rock, does not bring out the fragmental characters. N. H. w. 



No. 627. DIABASE. ( Amygdaloidal. ) 



Three-fourths of a mile west of Cross river. Forms an arched rock at the shore. 

 Ref. Annual Report, ix, page 32; Annual Report, x, page 61. 



Meg. This rock is hardly amygdaloidal, originally, but it contains many grains 

 of secondary minerals, such asstilbite, henlandite, thaliteandcalcite, making partially 

 a pseudamygdaloid. 



Mic. The rock is ophitic, with large augites which embrace numerous plagioclases. 

 The olivine is replaced by opaque ferruginous products. Thalite, with a very finely 

 fibrous structure, fills some spaces. 



One section. 



Age. Manitou. N. H. w. 



No. 628. DIABASE. ( Gabbroidal. ) 



Mouth of Manitou river. At this place about thirty feet of trap that shows red surfaces in falling to 

 pieces, lies on an amygdaloid conglomerate, the two together forming precipitous bluffs on either side of the 

 river, with lower stretches where the trap, which is somewhat basaltic, runs unbroken down to the water. This 

 kind of coast extends east at least to the west point of Pork bay and west to Little Marais. (Compare No. 160.) 



Ref. Annual Report, ix, pages 41, 42; Annual Report, x, pages 61, 63. 



Meg. Compact, medium grained, gray or grayish brown, with a slight tint of 

 chloritic green. 



Mic. The rock is not ophitic, yet the numerous augites were mainly thrust 

 aside by the generation of the feldspars so as to lie thickly alongside of the feldspars 

 in a pseudophitic embrace and are sometimes embraced within the feldspars. The 

 olivine is charged and the feldspars are stained by chloritic accumulations. 



One section. 



Age. Manitou. 



Remark. This rock was probably a surface flow, and assumed a basaltic colum- 

 nar structure in part, on cooling. A few small porphyritic augites can be seen in 

 the hand sample, but none are cut by the slide. N. H. w. 



No. 629. CONGLOMERATE. 



Mouth of Manitou river. 



Ref. Annual Report, ix, page 41; Annual Report, x, pages 61, 63. 



Meg. Crumbling, soft, red, amygdaloidal, the form and original structure of 

 the pebbles being obscured or lost. The pebbles are mainly of basic and sometimes 

 apparently of amygdaloidal trap, but occasionally they embrace a piece of red shale. 



Mic. The section, which is too thick, shows a scoriaceous rock, in the vesicles 

 of which are laumontite and calcite. 



One section. 



Age. Manitou. N. H w. 



