PETROGRAPHIC GEOLOGY AND DESCRIPTIONS. 243 



Amygdaloid. Diabase.] 



The shale is sandy and somewhat resembles No. 167, but contains a great deal of 

 laumontite. 



No section. 



Age. Potsdam. u. s. G. 



No. 178. AMYGDALOID. 



Six miles east of Temperance river. " Shows four feet, but beyond at another bluff rises so as to show 

 ten feet. It is a less amygdaloidal state of No. 177, and lies below No. 177. The last two numbers were got about 

 fifty rods east of Nos. 175 and 176. There is an isolated pillar of No. 176 standing on a broad pedestal rising 

 about twelve feet high, about forty feet from the shore. 



"Round the next little point, about twenty rods further, these beds are broken and confused, the dip 

 changing to the southwest. There are here broken upward bends, or domes, of soft amygdaloid that encroach 

 on No. 176 so as by weathering to make deep purgatories with buttresses of No. 176 separating them. After a 

 short interval the beds go back again, and retain the usual dip toward the lake. (Compare No. 626.)" 



Kef. Annual Report, ix, page 47; Annual Report, x, page 60. 



A brown, very fine-grained rock containing many amygdules of lieitkindite. 

 The lining to the amygdaloidal areas is bright red, and the heulandite sometimes 

 fills the whole amygdule and sometimes exists as crystals along the sides of the 

 amygdule. There are also a few amygdules of laumontite and some small areas which 

 seem to represent original, small, porphyritic feldspars now replaced by laumontite. 

 The rock is permeated by a soft, green to grayish mineral, probably thalite. There 

 is also present a dark-green, easily cleavable mineral in small areas; this is probably 

 chlorite. 



No section. 



Age. Manitou. u. s. G. 



No. 179. DIABASE (with olivine). 



" Comes in below these amygdaloids, at about a mile west of Poplar river; a greenish heavily bedded 

 doleryte; rising about ten feet and returning near the water, as the coast line crosses the strike of the beds." 

 Ref. Annual Report, ix, page 48. 



Meg. On a perfectly fresh fracture the rock is seen to have an oily lustre and 

 to be composed of a greenish, semi-transparent substance (plagioclase), and a reddish 

 or brownish material (augite). Scattered over the surface are small glistening faces, 

 probably of augite. There are many rather irregular areas (pseudamygdules) of a 

 soft green substance, probably thalite, and of a harder gray mineral with a radiating 

 structure. 



Mir. The rock is a fine-grained diabase, considerably altered, although much 

 of \befeldspar and augite are still preserved. There are some green areas (mostly 

 chlorite) surrounded and penetrated by hematite, which seem to be the remains of 

 olivines. The rock has been permeated with thalite, which is the most abundant 

 secondary mineral, and there is also a little th<nsoitife in the usual radiating forms. 



Two sections. 



Age. Manitou. u. s. G. 



