218 THE GEOLOGY OP MINNESOTA. 



[Diabase. Basalt. 



No. 141. DIABASE (with olivine). 



Dark green igneous rock, like No. 112, which holds the feldspar masses. This seems to lie under the 

 Palisades, as it conies in at once on the coast east of Palisade creek, the rock of the Palisades suddenly 

 disappearing with dip toward the lake; continues to near Baptism river. 



Ref. Annual Report, ix, pages 36, 39; Annual Report, x, page 139; Proceedings American Association for 

 the Advancement of Science, vol. xxx, page 162; Bulletin ii, pages 98, 99. 



Meg. A dark grayish brown diabase of rather coarse grain. The weathered sur- 

 face is filled with pits from which some mineral, probably olivine, has been removed. 



Mic. r/oyiorldxr. (iii/jite in large plates, and ma;/ net Iff, constitute the most of 

 the section. The rock is a diabase. Some areas of a green mineral, similar in 

 position and character to that described in Nos. 136 and 137, are present. There are 

 also dark brown, almost opaque, areas which are thought to represent original 

 olivines, now altered to the brown /><i/r//i/<//t/' seen in No. 133. Dr. Wadsworth 

 (Bulletin ii, page 99) says that this brown substance is closely like the hisingerite 

 of the Ovifak basalt. 



One section. 



Age. Cabotian. 



Remark. This rock is apparently part of the great mass which has been already 

 described as holding fragments of the anorthosyte in the vicinity of Beaver bay. 



U. S. G. 



No. 142. BASALT. 



Baptism river; N. W. % N. E. % sec. 4, T. 56-7 W.; 335 feet above lake Superior, and about thirty rods 

 above the fourth falls of the river. About one-fourth of a mile above this the river, and country generally, 

 undergoes a marked change, the former becoming slow and broad, and the latter level or undulating, without 

 visible rock in either. The rocks here consist of alternations of trap, or basalt, with amygdaloid, similar to the 

 layers of Agate bay, dipping N. W. 20. The lower beda of basalt form shelving points and bars across the river, 

 but the upper ones are in the bluff on the west side, which is thirty-five or fifty feet high. There are at least 

 sixteen beds of basalt, more or less distinct, but they are not so thick as at Agate bay. Here they are from three 

 to five feet thick, and all dip in the same direction. The fourth fall is made by one of these, more coarsely 

 crystalline than the others. 



Ref. Annual Report, ix, page 36. 



Meg. A very fine-grained, compact, dark gray rock. It has a few areas, 

 apparently amygdaloidal, of quartz and two smaller ones of a soft white substance. 



Mic. The section is composed of i>/(igiwlttfic microliths, small grains of aityifc, 

 iron ore, chlorite and confused, dirty, cloudy areas, which are in part at least alteration 

 products of augite. Quartz is present in minute grains all through the rock, and is 

 regarded as secondary. 



One section. 



Age. Cabotian. 



Remark. As noted above in the field description, this rock is one of the basalt 

 layers which alternate with amygdaloidal layers, as at Agate bay. The rocks here 

 are regarded as of the same age as those at Agate bay (see Nos. 94 to 102). The dip 

 to the northwest here seems to be anomalous. u. s. G. 



