162 THE GEOLOGY OP MINNESOTA. 



[Amygdaloid. Diabase. Calcite. 



In several irregularly shaped areas occurs a finely fibrous, yellowish green 

 mineral, which has much the appearance of that seen in No. 140 (7). It is in the 

 form of undulatory and mammullated layers, the fibres of which are perpendicular 

 to the layers and have parallel extinction and positive elongation. The name of this 

 mineral is not yet determined, but appears to be thalite. The mineral referred to 

 in No. 140 (7) is much harder than thalite. 



One section. 



A;/i'. Cabotian. N. H. \v. 



No. 77. AMYGDALOID (iritlt lniinn.ititf. > 



Overlies No. 76. A coarse amygdaloid, with liiuniimtite and calcite, containing some copper, wrought 

 slightly for copper at one time. Color, brown. 

 Kef. Annual Report, ix, page 23. 



The fragile /iimuoiifiie nests are of various shapes and sometimes two inches in 

 larger dimension, the fibres radiating from points; color, light flesh-red. The fibres 

 are optically negative, and have extinctions at 6 to 24. The rock is a fine olivinitic 

 diabase in which the augite preceded the feldspar and was then corroded. 



One section. 



Aye. Cabotian. N. H. \v. 



. No. 78. DIABASE. 



Forms the bite of Crystal bay east of Lester river. Bluffs fifteen to twenty feet in hight. 

 Eef. Annual Report, ix, page 23; Annual Report, x, page 38. 



Mey. Firm, brownish red,, much jointed, disintegrating and falling in large 

 masses, weathering light red or pinkish ; containing nests of calcite crystals. 



Mic. The section shows a fine-grained diabase now considerably altered and 

 impregnated by iron oxides, apparently both magnetite and hematite. The plagio- 

 clase laths are usually still distinct, though clouded. One of these, cut nearly per- 

 pendicular to the axis of least elasticity, gave an extinction angle of 21, indicating 

 fiibrtHloi-ite. Secondary quartz in small grains is common. There are some pseud- 

 amygdaloidal areas filled with dilorH/' and quartz. 



One section. 



Aye. Cabotian. u. s. G. 



No. 78 A. CALCITE.. ( Crystals from No: 78. ) 



l\ef. Annual Report, ix, page 23. 



These nests are sometimes eighteen inches across, but generally less than ten. 

 The forms are sometimes perfect, with double terminations. They are impacted in 

 a fine red clay, which doubtless has infiltrated through the loose rock from the 

 surface above, where a continuous sheet of the same red clay covers the country. 



N. H. W. 



