250 THE GEOLOGY OP MINNESOTA. 



[Basalt. Diabase. 



No. 195. BASALT. (Amygdaloidal.) 



From the north side of the first little creek in Good Harbor bay. Although not seen to immediately 

 underlie No. 194, it is evident, from the remnants of No. 194 which fill the cracks in No. 195, that these rocks 

 belong together. 



Ref. Annual Report, ix, pages 51, 52. 



Meg. This is apparently the upper surface of an amygdaloidal trap flow. Some 

 of the cavities are flattened or roughly tubular, with their greater dimensions hori- 

 zontal. Some are filled with quartz, some with laumontite, and some with a green 

 tibro-lamellar mineral resembling delessite. Its own upper surface was apparently 

 broken up, and its fragments were cemented again in xitu. Its general color is 

 brown, but the amygdaloidal minerals give it a spottedness. It is finely compact 

 when not amygdaloidal. 



No section. 



Age. Manitou. N. H. w. 



No. 196. DIABASE. (Amygdaloidal.) 



From the small rocky island off the point that encloses Good Harbor bay. -In line of bearing of No. 193. 

 Ref. Annual Report, ix, page 51. 



Meg. A fine-grained, gray rock, with numerous radiated flesh-red and white 

 zeolitic hard minerals, which have been widely distributed as thomsonites. 



Mi<: Throughout the section is disseminated much of the glassy residuum, 

 now mostly filled with feebly polarizing microliths. 



There are feldspars' though they are small and imperfectly developed, and 

 there are auyites that separated early from the magma, and hold many inclusions. 

 The rock is essentially the same in kind as No. 193, in which ftoir/hif/ite is evident 

 and abundant. In this rock, however, unlike that, there is much of the tlialite stage 

 or phase, mentioned under No. 162, as a possible alteration product from olivine. 

 This is seen in the form of minutely radiated fibrous coatings that surround some of 

 the areas, and frequently in the fillings of cavities of considerable size. In the latter 

 condition, this substance is greenish, and although the general aspect is amorphous, 

 and the polarization is that characteristic of a felted mass, yet on close inspection it 

 is apparent that even the little scales or particles which make up these larger 

 patches are occasionally fibrous and positive in elongation in the manner of those 

 coatings in which the fibration is more coarse and more evident. In keeping with 

 this fact is the light greenish alteration product of many minute olivines. These 

 greenish grains are accompanied by much ferruguinous coloring matter, which 

 surrounds them and penetrates them irregularly as if accumulated along the former 

 irregular fracture planes of olivine. These grains are plainly altered olivines. They 

 are nearly dark during rotation between the nicols, but not wholly so. They exhibit 

 no cleavage like that described under No. 193, nor any absorption. In other words, 



