PETROGRAPHIC GEOLOGY AND DESCRIPTIONS 1{)1 



Calcite. Amygdaloid. Tuff.] 



wanting. Hematite, and especially magnetite, have accumulated in these areas, the 

 latter disposed in parallel bars, as if it occupied the spaces of former cleavage open- 

 ings. Indeed in some places the prismatic cleavage of a pyroxene is simulated in 

 the angles presented by these rods of magnetite. The feldspars are also sometimes 

 somewhat colored by a hematitic powder, and usually are much affected by incipient 

 alteration, which renders it useless to attempt to further define them than to say that 

 they are probably labradorib-. 



The pyroxene ( ?), changed as above described, was a very abundant ingredient, 

 on the supposition that the grains which embrace, the feldspars ophitically, and are 

 reddened by hematite, are of pyroxene. 



Olivine, now wholly serpentinized so as to give a close, greenish, almost opaque, 

 polarization, is quite common in this rock. These grains are uniformly embraced in 

 a coating of magnetite, and sometimes they are colored within by hematite. 



One section. 



Age. Cabotian. 



Remark. The interesting feature about this rock is the fact that instead of 

 chloritic secondary products, as a result of alteration of the pyroxene, the product is 

 reddish and brownish, with very little and often no chlorite visible. It may hence 

 be of the nature of a residuum of the magma. N. H. w. 



No. 60A. CALCITE. 



Duluth. Same locality as No. GO. 

 Ref. Annual Report, ix, page 20. 



Meg. " Dog-tooth crystals of calcite which occur in a finely-jointed or brec- 

 ciated condition of No. 60, which occurs suddenly, like a dike, extending up and down 

 across the face of the bluff. This breccia is about twenty feet wide and the char- 

 acters of No. 60 return on the east of it." The crystals contain a considerable amount 

 of impurities. The largest crystal is near two and a half inches in length. 



No section. 



Age. Calcite crystals in Cabotian porphyryte. u. s. G. 



No. GOB. AMYGDALOID. 



East Duluth. West of London. Same place as No. 60. 

 Ref. Annual Report, ix, page 20. 



This is an amygdaloidal portion of No. 60. Besides abundant calcite the amyg- 

 dules contain epidote, resinous garnets (?) and quartz. 



No section. N. H. w. 



No. 61. TUFF. (Hnhnun-'me.) 



East Duluth. Six rods west of a massive overhanging bluff, and at the eastern limit of No. 60, two feet 

 thick, in a lot of thin beds, with a definite dip of 24 in a direction N. 60 E. 



Ref. Annual Report, ix, page 20; American Geologist, vol. xviii, pages 211-213. 



