ARCHEAN IN^ FELCH MOUNTAIN DISTRICT. 



391 



result of the pressure that has affected their optical properties. The 

 evidence is quite clear that the minerals now present have crystallized in 

 parallel elongated forms, and it is to this they owe their prevalent lamina- 

 tion even when the color banding is indistinct or wanting. 



Subsequent to the time of crystallization they have been exposed to 

 the action of great stresses, which not only have left a record in the strains 

 now frequently perceptible in the minerals of the early crystallization, but 

 also in many cases have produced roughly parallel fractures and fracture 

 zones sometimes coinciding with and sometimes oblique to the early lami- 

 nation. In these zones coarse micas have grown, reenforcing the old 

 lamination when parallel to it, and when oblique producing a less regular 

 secondary foliation, which is entirely analogous and probably contempo- 

 raneous with the foliation of the crushed granites. 



The following analyses of these gneisses are interesting as showing 

 their striking chemical relationship to the granites (analyses of which are 

 given on p. 389), with which they are intimately associated : 



Analyses of gneiss. 



[By Dr. H. S". Stakes, U. S. Geol. Survey.] 



'Water not determined. 



'Includes PjOs. 



' Ba, Sr, Li, CI, S, SO3 were not looked for. 



No. 1. Specimen 34826, Lalie Superior Division, U. S. Geol. Surv., 240 N., 1,250 W., sec. 35, T. 42 N., 

 R. 29 W., Upper Peninsula of Michigan. 



No. 2. Specimen 36058, Lake Superior Division, U. S. Geol. Surv., 325 N., 1,225 W., sec. 36, T. 42 N., 

 E. 29 W., Upper Peninsula of Michigan. 



No. 3. Specimen 36080, Lake Superior Division, U. S. Geol. Surv., 15 N., 1,025 W., sec. 31, T. 42 N., 

 R. 28 W., Upper Peninsula of Michigan. 



