270 THE GEOLOGY OF MINNESOTA. 



[Diabase. Aporhyolyt*. 



Meg. A fine-grained, compact, heavy, dark gray, almost black rock, looking like 

 a fine-grained diabase. There are some porphyritic, gray to reddish feldspars, which 

 are more common on one half of the hand specimen than on the other. 

 No section. 



Age. Cabotian. u. s. G. 



No. 228. DIABASE. ( Gabbroidal. ) 



From the broad point just west of Cannon Ball bay; S. E. ^ sec. 6, T. 62-5 E. " The east side of this bay 

 is made of the same rock, also the east point, also the island east of it; the coast being rocky and low, or rising 

 from six to ten feet, basaltic. The next island, and the coast along, especially the points of the coast, are of the 

 same. It rises into basaltic beds in a sharp point [S. E J4 S. W. J4 sec. 31, T. 63-5 E.] on the west side of Bed 

 Rock bay." 



Ref. Annual Report, ix, pages 57, 58; Annual Report, x, page 43; Bulletin ii, page 99. 



^f^'(j. A rather coarse-grained, heavy, black diabase. There are numerous 

 yellowish grains, which might be taken for olivine, but the section shows no olivine. 



Mir. A beautiful section of a rather coarse-grained, fresh diabase. Some of 

 the auyite has a tendency to an idiomorphic development, and is thus earlier than 

 some of the feldspar, but most of the augite is later than most of the feldspar. There 

 is a considerable amount of a brown alteration product (bowlingite) present. Dr. 

 Wadsworth (Bulletin ii, page 99) regards this as an alteration product of an inter- 

 stitial basaltic base. It is also apparent that some of it originated from the pyroxene. 



One section. 



Age. Cabotian. 



Remarks. For further description, see under Nos. 222 and 223, which are 

 evidently from the same mass as this specimen. (See, also, under Nos. 133 and 229.) 



t U. s. G. 

 No. 229. DIABASE (with olivine). 



From Red Rock bay; runs under the Eastern Palisades.* 



Ref. Annual Report, ix, page 58; Annual Report, x, page 140; American Association for the Advance- 

 ment of Science, xxx, page 163. 



Mry. This rock greatly resembles No. 228, but is finer grained. 



Mic. An ophitic diabase with much fresh olivine. The rock is fresher than 

 No. 228, both in respect of the augite and the possession of unchanged olivine. The 

 augite appears chiefly in ophitic relation to the feldspar; but there is plainly an 

 older augite which is not diallagic but filled with dark opaque particles scattered 

 like dust throughout their mass. These have independent outlines like those of 

 No. 228. 



One section. 



Age. Cabotian. N. H. w. 



No. 230. APORHYOI.YTE. 



Red Rock bay; sec. 34, T. 63-5 E. The rock of the Eastern Palisades. (See No. 620.) 

 Ref. Annual Report, ix, pages 58, 59; Annual Report, x, page 59. 



*The Eastern Palisades are N. W. Ji S. E. % sec. 34, T. 63-5 E. 



