238 THE GEOLOGY OF MINNESOTA. 



[Diabase. 



Mic. Section of the upper part of one of the wrinkles shows a finely microlitic, 

 somewhat divergent crystallization of the feldspar, before which, however, there was 

 a generation of small oJi vines. No augite is visible, but the intervening spaces are 

 filled with a red substance which represents the poorly differentiated base. In this 

 are glass, hematite spicules, and magnetite grains. The section between closed nicols 

 is darkened by the prevalence of this residuum. 



One section. 



Age. Manitou. N. H. w. 



No. 171. DIABASE (with olivine). 



From the lowest layer exposed at the falls of Temperance river, about one mile from the lake. This fall 

 is on the N. E. % sec. 30, where a little creek joins the river from the northwest. 

 Ref. Annual Report, ix, page 45. 



Meg. Rather dark-brown and heavy trap, somewhat amygdaloidal, much 

 decayed, holding greenish-gray pseudamygdules apparently of thalite; also of calcite 

 and of quartzine(?) 



Mic. The rock is ophitic, the olivine is considerably altered to boirHnyite, the 

 augite rather fresh, and the feldspars are clear. The prevalence of thalite in this rock 

 is an indication of great change, but the rock does not seem to show it except in the 

 olivine. 



Age. Manitou. N. H. w. 



No. 172. DIABASE (with olivine). 



" About three-fourths of a mile below the mouth of Temperance river; from a layer of trap that weathers 

 green, is irregularly bedded and in spots is amygdaloidal. This is a little higher than No. 166, in the bedding, 

 but at points further east, and particularly at a point about one-third of a mile east of Temperance river, seems to 

 hold large globular masses, as if of boulders, and at other places seems to be conglorneritic in the same way." 



Kef. Annual Report, ix, page 46. 



Met/. A fine-grained, greenish-brown, diabasic rock, which has been permeated 

 by a gray to green, soft mineral supposed to be thalite. The greenish color of the 

 rock is due to the great abundance of this mineral. 



Mic. A fine-grained diabase, holding plagioclase, augite, magnetite, hematite, 

 chlorite and thalite. The last named mineral is common in small pseudamygdaloidal 

 areas throughout the section. It is cloudy, and has a minutely fibrous radiating 

 structure. There are also some areas which probably represent olivines, of an opaque 

 substance, sometimes brown and semitransparent, which is perhaps boirlingite. The 

 augite is not nearly as much altered as one would expect from an examination of 

 the hand sample. 



One section. 



Age. Manitou. u_ s _ G> 



