248 THE GEOLOGY OP MINNESOTA. 



[Diabase. Basalt. 



No. 191. DIABASE (luith olivine) . 



Cascade river. This rock first appears on the east of Cariboo bay, and continues to Cascade river, form- 

 ing a low coast. It overlies No. 192. 



Ref. Annual Report, ix, page 50. 



Mey. Gray, mottled, coarse grained; evidently a normal diabase. 



Mic. The ophitic relation between the auyite and (hs feldspars is evident at a 

 glance. The oli vines are much changed to buirlhujite. There is a considerable amount 

 of a yellowish-green substance occupying positions that indicate that it formed after 

 the other minerals, which probably represent altered remnants of the basic magma, 

 never differentiated. A little magnetite is seen. 



Two sections. 



Age. Manitou. N. H. w. 



No. 192. BASALT. 



Right bank of Cascade river, at the lake shore; a low outcrop. Underlies No. 191. 

 Ref. Annual Report, ix, page 50; Annual Report, x,page 59. 



Meg. Fine grained, brown, scantily amygdaloidal and pseudamygdaloidal with 

 calcite and laumontite, the latter mineral also coating the joints. 



Mic. The feldspar microliths are compactly embraced in an opaque matrix 

 which was probably at first a glassy substance. A small amount of yellowish-green 

 thalite is scattered throughout the rock. This rock was evidently from near the 

 surface of a lava flow. 



One section. 



Age. Manitou. N. H. w. 



No. 193. DIABASE (with mesolite and tfiomsonite). 



From the very point which sharply encloses Good Harbor bay, i. e., Terrace point. 



Compare No. 535. 



Ref. Annual Report, ix, page 51; Annual Report, x, page 42. 



Meg. Dark, heavy, rather coarse amygdaloid. 



Mic. The white tJioii/xoniffs are intimately mingled with more or less reddish 

 mesolites. These zeolites are closely intergrown in the same round cavities. The thom- 

 sonite is distinguished by its bright polarization in contrast with the very low or non- 

 polarizing quality of the mesolite. A thick section of the finely fibrous mesolite gives 

 no coloration, and in ordinary light it is clouded with fine hematitic or other dust. 

 Sometimes, suddenly, in the midst of such an obscuration, other coarser, nearly par- 

 allel, lamellae or fibres flash out with brilliant colors characteristic of thomsonite, 

 while at the same time such coarser fibres are translucent and free from impurities 

 in ordinary light. This intergrowth is also sometimes differently alternated. Even 

 with the naked eye the centres of some of the broken amygdules can be seen to be 

 coarser than the rest. It is plain that for some reason the cavities were partly filled 



