AEGHEAN IN FELCH MOUNTAIN DISTRICT. 387 



steep slopes, which are frequentl}^ escarpmeut-hke iu character, and for 

 short distances present smooth faces to the valley. In sec. 33, T. 42 N., 

 R. 28 W., the mural face which runs southeast across the eastern half 

 of the section with the regularity of a ruled line is a true fault scarp. 

 Toward the western end of this valley, in sec. 32, T. 42 N., R. 29 W., 

 the floor gradually rises and the swamp area broadens, penetrating the 

 Archean in a network of thicker and thicker mesh about the higher hum- 

 mocks, until these are finallj^ overtopped. 



PETROGRAPHICAL CHARACTERS. 



The rocks of the Archean areas may be divided into four quite distinct 

 types, namely: (1) Granites or granitic gneisses, (2) gneisses with banding 

 or distinct lamination, (3) mica-schists, and (4) hornblende-gneisses or 

 amphibolites. Between the first two divisions there is an extremely close 

 mineralogical and chemical likeness, while in these respects the fourth 

 division stands against all the others in strong contrast. 



(1) The granites of the first division are, as seen in the field or in the 

 hand specimen, holocrystalline rocks of fine to medium grain, in which the 

 eye can readily distinguish the presence of quartz, pink feldspar, muscovite, 

 and biotite. In color they are prevailingly of pink or reddish tints of light 

 shades. Structurally, they frequently appear in small areas to be entirely 

 massive, but even in the most massive occurrences the hammer can usually 

 part them along roughly parallel surfaces which glisten with spangles of 

 mica, indicating a certain degree of alignment in these constituents. Gen- 

 erally, however, a rude foliation is more or less distinctly visible, and is 

 sometimes exceedingh^ well developed, even to the point of fissility. It is 

 always apparently due to the parallel arrangement of the micas, which 

 are more abundant as the foliation becomes more distinct. 



The field relations sliow that the massive and more or less, foliated 

 varieties of this division are closely bound together by indistinguishable 

 gradations and, indeed, often constitute a visibly integral mass. The usual 

 arrangement of the micas is not parallel to a surface but parallel to a line 

 which is generally inclined to the horizon at angles varying between 10° 

 and 35°. A hand specimen when turned about the direction of foliation as 



