446 



THE GEOLOGY OP MINNESOTA, 



[Slate. Diabase. Gneiss. 



613 



labradorite, and the olivine appears to be older than either. However, one com- 

 pound olivine grain was seen which was later than some of the surrounding feldspar. 







This structure in rock No. 258 (Hat point) is illustrated on page 285. 



Age. Cabotian. u. s. G. 



\YCST POINT or THE BJ\*. EAST POINT or THE: BAY. 



FIG. 80. LITTLE PORTAGE BAY, PIGEON POINT. 



No. 604. SLATE. 



Near the "little portage" on Pigeon point, south of the dike (No. 605) on the point next east of the little 

 bay on the south shore whence the portage starts out. The portage trail is eighty-seven paces from shore to shore. 

 Ref. Annual Report, ix, pages 69, 70; Annual Report, x, page 57. 



Meg. Fine grained, black, with conchoidal fracture, a hardened fragmental. 



Mic. The section shows angular quartzes, also sub-rounded, impacted in an 

 ill-defined matrix, which is dark, and evidently holds some iron oxides and other 

 opaque substances. One section. 



Age. Animikie. 



Remark. Figure 30 shows the structural relations of rocks Nos. 604 to 616. 



N. H. W. 



No. 605. DIABASE (ivith olivine). 



Little portage of Pigeon point. A dike twenty-five feet wide, cutting the slates and quartzyte; south end 

 of the portage. 



Ref. Annual Report, ix, pages 69, 70; Annual Report, x, page 57. 



Meg. Medium-grained diabase. 



Mic. The augite is, in part, distinctly and beautifully ophitic on the feldspar, 

 but in part also was earlier than the feldspar. The rock is fresh. One thick section. 

 Age. Cabotian intrusive in the Animikie. N. H. w. 



No. 606. GNEISS (ivttlihyperstliene). 



Rock extending next north of the dike No. 605, in contact with it, but forming the surface. 

 Ref. Annual Report, ix, pages 69, 70; Annual Report, x, page 57; Wadsworth, Bulletin ii, Minnesota Geo- 

 logical Survey, page 120. 



Meg. The rock is medium-grained, uniform, "pepper and salt " color. 



Mic. Consists largely of secondary quartz in form of micropegmatyte in the 

 feldspars and of isolated grains of much altered feldspar, whose triclinic nature can 

 hardly be established, owing to a cloudy and grayish diffusion of alteration products 

 through it, of hornblende, which is greenish, fibrous, and somewhat dichroic, of biotite, 

 apatite, chlorite, and perhaps other secondary minerals, the whole indicating a meta- 

 morphic condition of a clastic rock or a silicified selvage of a basic one. Two sections. 



