276 THE GEOLOGY OF MINNESOTA. 



[Basalt. Diabase. 



No. 243. BASALT (ivitli olivine). 



From the west point of Deronda bay; N. W. M N - w - M sec. 30, T. 63-6 E. 

 Ref. Annual Report, ix, page 60. 



Meg. Fine-grained, hard, nearly black, homogeneous rock. It is rather bedded, 

 but not basaltic, lying on an amygdaloid (No. 244). 



Mic. The thick section is only sufficient to show that this rock is essentially 

 one of the series to which No. 235 belongs. It holds some calcite and some quartz. 



One section. 



Age. Cabotian. N. H. w. 



No. 244. DIABASE. ( Amyydaloidal. ) 



From the west point of Deronda bay. A reddish brown amygdaloid with green amygdules, underlying 

 No. 243, passing irregularly into No. 245, which is mainly non-amygdaloidal, but has nests of a lighter mineral; 

 probably of the series represented by Nos. 232-235, 237-242. 



Ref. Annual Report, ix, page 60. 



Mac. Reddish-brown, rather fine-grained, spotted with fine green amygdules, 

 resembling No. 232 and that series. 



Mic. A diabase, with lath-shaped feldspars, magnetite and altered minerals 

 which cannot be determined from the section. 



The amygdules are of a green substance, finely radiated, and having a positive 

 extinction, i. e., parallel with the fibres, and seem to belong to antigorite (Mineralogie 

 de France, vol. i, page 426), or to delessite. The fibres are parallel with n s . A 

 Boricky test, however, was made to detect the possible presence of potassium, by 

 which celadonite differs from antigorite, with the result that no potassium was found. 



One section. 



Age. Cabotian. N. H. w. 



No. 245. DIABASE. 



West point of Deronda bay; N. W. % N. W. 14 sec. 30, T. 63-6 E. Is mainly non-amygdaloidal. Passes 

 into No. 244. 



Ref. Annual Report, ix, page 60. 



Meg. A dark-gray, compact, fine-grained, diabasic rock. The hand sample 

 shows very fine, indistinct, yellowish to greenish amygdules. 



Mic. A fine-grained diabase, with alteration products, mainly chlorite. The 

 augite is not abundant, but usually occurs in plates of considerable size, including 

 the plagioclases. The rock is very rich in plagioclase, there being considerable areas 

 where the augite is lacking; here the plagioclase is in ill-defined laths and allotrio- 

 morphic grains. A few small green areas, probably representing original olivine, 

 are present. 



One section. 



Age. Cabotian. u. s. G. 



