PETROGRAPHIC GEOLOGY AND DESCRIPTIONS. 617 



Dioryte. Gneiss.] 



No. 971. DIORYTE. 



Schistose part of the same dike as No. 969. 

 Ref. Annual Report, xv, pages 337, 391. 



Mi'g. Rock similar to No. 970, in sharp contact with a coarse-grained, gray, 

 hornblende syenyte. 



Mic. The section was made from the syenyte. It is composed essentially of 

 feldspar, commonly clouded, and hornblende. 



One section. 



Age. Archean. u. s. G. 



No. 972. GNEISS. (Granitoid,.) 



Prom a point a little north of No. 969. 

 Ref. Annual Report, xv, pages 337, 392. 



Meg. A fine-grained, gray, biotite granite or granitoid gneiss. The hand 

 sample does not show the gneissic structure of the rock very markedly. 



Mic. The section shows an ordinary granite, the essential minerals being 

 feldspar, quartz and biotite. 



One section. 



Age. Archean. u. s. G. 



No. 973. GNEISS. (Dioritic.) 



"Hornblende gneiss, a phase of No. 972, from the northwest corner of sec. 30, T. 61-12." Birch lake. 

 Ref. Annual Report, xv, pages 338, 392. 



Meg. Medium-grained, dark-gray, dioritic rock. Parts of the specimens are 

 light colored, but the gneissic structure is not well shown in the hand samples. 



Mic. The section shows a granitoid rock the essential minerals of which are 

 hornblende and feldspar. The latter mineral is usually much clouded by kaolinization. 

 One section. 



Age. Archean. u. s. G. 



No. 974. GNEISS. (Dioritic.) 



"Shows the same rock (No. 972) undergoing a change toward mica schist; from the same locality." 

 Ref. Annual Report, xv, pages .338, 392. 



Meg. A dark-gray, rather fine-grained, roughly schistose rock. 



Mic. The section is in general similar to that of No. 973. One section. 



Age. Archean. u. s. G. 



No. 975. GNEISS. ( Dioritic. ) 



"Two other samples of No. 972, here a mottled schist, from the extreme west end of Birch lake, south of 

 the mouth of Birch river." 



Ref. Annual Report, xv, pages 339, 392. 



Meg. A gneissic rock, varying in color, composed mainly of feldspar and 

 hornblende. 



