460 THE GEOLOGY OF MINNESOTA. 



[Diabase. Amygdaloid. Basalt. 



No. 630. DIABASE. 



Two miles west of Little Marais point; forms perpendicular cliffs. Resembles the rock of Eclipse beach. 

 Ref. Annual Report, ix, page 41; Annual Report, x, page 62. 



Meg. Grayish, with medium grain. 



Mic. Ophitic, and charged with thalite. The olivine is lost. The abundant 

 thalite in a thick section shows, along with parallel extinction, a coloration about 

 the same as the plagioclase, but a trifle higher. 



One section. 



Age. Manitou. 



Remark. This probably lies below the Little Marais conglomerate, since the 

 heavy trap sheet on the east point of Little Marais, which lies on the. conglomerate, 

 strikes (westward) from the shore at an angle and disappears in the lake, letting the 

 western shore line on to lower strata. 



No. 631. AMYGDALOID. 



Same place as No. 630. 



Ref. Annual Report, ix, page 41; Annual Report, x, page 62. 



MC<I. The cavities are filled with thalite and calcite, the latter lying frequently 

 within the former. 



Mic. The rock is ophitic, and was evidently the superficial portion of an erup- 

 tive flow. One section. 



Age. Manitou. N. H. w. 



No. 631A. BASALT (?) 



From No. 631. Occurs in the form of veins accompanied by stilbite and calcite. Seems to be foreign to 

 No. 631. 



Ref. Annual Report, x, page 62. 



Meg. Very dense, brown or reddish brown. 

 No section. 



Age. Manitou. N. H. w. 



No. 632. BASALT. 



From a point of rock on sec. 29, T. 57-6, separated from the green trap No. 630 by a conglomerate thirty- 

 five feet thick. Thickness, twelve feet. 



Ref. Annual Report, ix, page 41; Annual Report, x, pages 62, 63. 



Meg. Dark, brownish red, dense, blotched with red, on account of the red partings 

 along all the joints, crossed by siliceous red seams and veins like those seen in No. 

 631, and contains large lumps and geodes of quartz. 



Mic. The minute feldspars and augites lie in an abundant residuum of the 

 magma, which appears to have been consolidated as a glass,, but is now filled with 

 indistinct crystalliths. 



One section. 



Age. Manitou. N. H, w, 



