PETROGRAPHIC GEOLOGY AND DESCRIPTIONS. 129 



Vein matter. Aporhyolyte.] 



Meg. A fine-grained, brown-weathered condition of No. 32. Perhaps was at 

 first largely of glass. It is now permeated with epidote and calcite. N. H. w. 



No. 32B. VEIN MATTER ( from No. 32 J. 



Ref. Annual Report, ix, page 15; Annual Report, x, page 141. 



Greenish, fine grained, consists of epidote, calcite, quartz, leucoxene, some of the 

 last showing the sagenite structure, plagioclase (albite ?). These minerals all appear 

 as fragments, somewhat rounded, and without any evidence of vein structure. 



One section. N. H. w. 



No. 33. AMYGDALOID. 



Duluth. About sixty feet east of No. 32, on the east side of a fault, near the lake level. The cavities and 

 the fissures have been generally filled with epidote and calcite, with a layer of greenish segregated material, 

 probably delessite, lining each cavity nearest the rock. 



Ref. Annual Report, ix, page 15. 



No section. N. H. w. 



No. 33 A. APORHYOLYTE (?) 



Duluth. From patches in No. 33. 

 Ref. Annual Report, ix, page 16. 



Meg. A reddish compact aphanitic rock with a few apparent amygdules. On 

 one side two of these extend out from the rock, and appear somewhat like pebbles. 



Mic. Very minute feldspar microliths are scattered through a groundmass 

 which is composed of irregular ill-defined areas of quartz. This quartz contains the 

 microliths and the minerals of the groundmass poikilitically (see No. 42). The rest 

 of the groundmass, aside from the quartz, is composed of epidote, chlorite, magnetite 

 and minute red particles (hematite). 



One section. 



Remarks. It is not certain just what this rock is, but it is thought to be a 

 devitrified lava, perhaps as acid as a trachyte. 



Age. Cabotian. u. s. G. 



No. 33B. PORPHYRYTE. ( Amyrjdaloidal. ) 



Duluth. Taken from the stratigraphical equivalent of No. 33. 



Ref. Annual Report, ix, page 16. Proceedings American Association for the Advancement of _Science, 

 vol. xxx, page 164. 



Meg. A brown, very fine grained rock, containing many red, porphyritic 



feldspars; also considerable epidote. 



Mic. The section is poor. It shows very few of the porphyritic feldspars, and 

 these are highly altered. The groundmass contains small lath-shaped feldspars and 

 the usual alteration products. There is also present a considerable amount of very 

 fine grained material between these feldspars. This probably is largely quartz. 



One section. 



Cabotian. u. s. o, 



10 



