246 THE GEOLOGY OF .MINNESOTA. 



[Diabase. 



areas, apparently pseudamygdules, of calcite and thalite. The other sample repre- 

 sents the smooth-weathering portion; it is similar to the first but contains no calcite 

 and no, or comparatively little, thalite. It is, however, more or less permeated by 

 a soft, green material. 



Mir. The rock is a fine-grained diabase with large amounts of hematite. The 

 aiif/ite andplagioelase are much less altered than would be expected in a rock of this 

 character in fact all of the diabases along this part of the coast from Manitou river 

 eastward, except No. 176, appear considerably decayed in hand specimens, but in 

 thin sections they are seen to be comparatively fresh. There are pseudamygdules 

 of t halite scattered through the section. Another section, marked No- 186 (?), is of a 

 similar rock and was perhaps made from the smooth weathering hand sample. 

 Instead of having pseudamygdules of thalite this section has pseudamygdules of 

 chlorite. 



Two sections. 



Age. Manitou. u. s. G. 



No. 187. DIABASE. ( Amygdaloidal, with olivine.) 



Eclipse beach, sec. 26, T. 60-3 W. 



Ref. Annual Report, ix, page 49; Annual Report, x, page 60. 



Meg. A dark, brownish gray, fine-grained, diabasic rock, with amygdules of 

 stilbite, a soft dark green mineral, a white radiating mineral, apparently similar to 

 No. 163A, and calcite. Each of the first two minerals fill amygdules by themselves, 

 while the last two are usually found associated with the green mineral. The rock 

 contains one large crystal of feldspar which is apparently similar to the labradorite 

 of the anorthosytes; this crystal is three-fourths of an inch across. 



Mic. A fine-grained diabase, with the augite frequently in plates of considerable 

 size. A large amount of olivine, now changed to brown loir/iityite (?) and a green 

 chloritic material, is also present. The section shows some of the stilbite amygdules 

 and also the green mineral. The latter was called delessite in the field, and it is also 

 here referred to that mineral; it occurs in minute fibres, which are elongated 

 positively, radiating in bands from the sides of the amygdule; it is greenish in 

 ordinary light, has very low double refraction and is hardly pleochroic. 



Age. Manitou. 



Remarks. This rock is similar to No. 625, and the radiating white mineral is 

 similar to No. 625A. u. s. G. 



No. 188. DIABASE (with olivine). 



Eclipse beach, sec. 26, T. 60-3 W. Occurs suddenly at first, on a point running northeast (Eclipse beach) 

 and enclosing a little bay, being a bed of overflow of igneous rock, with corrugated upper surfaces like those 

 seen at the mouth of Temperance river (figure 17), especially at points further east where it becomes closely 



