PETROGRAPHIC GEOLOGY AND DESCRIPTIONS. 811 



Diabase. Breccia. Feldspar schist.] 



Mic. The slide only shows a coarsely ophitic diabase or gabbro, like that at 

 Short Line Park. Owing to weathering decay, numerous secondary minerals of the 

 usual species have been developed, in which epidote is most conspicuous. Red 

 hematitic spots are loosely disseminated, but there seems to be no difference in the 



I 



essential mineral composition. One section. 



Aye. Cabotian (boulder). N. H. w. 



No. 1951. DIABASE. 



First hill range of gabbro, i. e., most westerly, at Short Line park, at the railroad cut of the St. Paul and 

 Duluth railroad. 



Ref. Annual Report, xxii, page 15. 



Meg. Intended to show the average amygdaloidal structure. 



Mic, The green spots supposed to be due to amygdaloidal structure are occupied 

 by chloritic and actinolitic fine aggregate, or by this aggregate more or less replaced 

 by fine interlocking secondary feldspars (or quartz). One section. 



Age. Cabotian (probably Beaver Bay diabase). N. H. w. 



No. 1952. DIABASE. 



"One of the narrow amygdaloidal dikes cutting this hill, with contact on the gabbro; same place." 

 Ref. Annual Report, xxii, page 15. 



Meg. The country rock, with which the dike is in contact, is a rather fine 

 grained, gray diabase with white feldspars. The dike rock is a very fine-grained, 

 dark-gray diabasic rock. No section. 



Age. Dike cutting Cabotian (Beaver Bay diabase?). u. s. G. 



No. 1956. BRECCIA. 



" A breccia, embracing some green fragments of the schist." West Breitung mine, Soudan. 

 Ref. Annual Report, xxii, page 16. 



Mey. A rough breccia of green schist and hematite cemented by hematite. No 

 section. 



Age. Archean (Keewatin). u. s. o. 



No. 1957. FELDSPAR SCHIST. (Calcareous.} 



North side of Ely island, Vermilion lake. 

 Ref. Annual Report, xxii, page 1G. 



Meg. Light colored, nearly white, not very siliceous. 



Mir. The slide is very largely composed of feldspar and calcite, with only one 

 small quartz grain, so far as discoverable. This feldspar is in two conditions, viz., old 

 crystals now almost entirely lost by alteration, and fragments of crystals. These 

 are thickly strewn with calcite and with feldspar of the second form, viz., micro- 

 granulitic interlocking grains. This feldspar seems to have formed pari passu with 



