266 THE VERMILION IRON-BEARING DISTRICT. 



DISTRIBUTION, EXPOSURES, AND TOPOGRAPHY. 



Distribution. — This granite is confined in its occurrence to Saganaga 

 Lake and its vicinity. It covers about 100 square miles in Minnesota, but 

 only a portion of its area is shown on the accompanying map (PI. II). 



JExposures. — Within this area its exposures are very numerous, for the 

 country is in many places comparatively bare of vegetation, the drift is as 

 a rule thin, and the presence of large bodies of water — Saganaga, West 

 Gull, and Red Rock lakes and their tributary streams — insure frequent 

 exposures on the shore of the mainland and on the islands. 



Topography. — The topography of this granite area offers a strong con- 

 trast to that of the surrounding country. In the surrounding teiTitory, 

 which is underlain by Archean greenstones and Lower Huronian sediments, 

 the topography is rough, being marked by prominent hills, generally, to be 

 sure, having the round contours characteristic of glaciated areas, but often 

 presenting high and rugged clifFs. Within the granite area the topographic 

 features are, for the most part, not strongly emphasized. The hills are low 

 and rounded and the hilltops seem to approach very nearly the same level, 

 so that in looking over this area from some of the higher surrounding 

 elevations one gets an idea that this particular portion of the district has 

 been reduced very nearly to a peneplain. 



PETROGRAPHIC CHARACTERS. 



Macroscopic characters. — This granite is very coarse grained over a large 

 portion of the area in which it occurs and is usually developed as a granite- 

 porphyry in which the phenocrysts are large quartzes. However, as one 

 traverses the reg'ion from West Gull Lake through Red Rock to Saganaga 

 Lake — that is, as one goes approximately from the periphery toward the 

 center of the area — it is very noticeable that the grain of the rock, which is 

 relatively fine upon the exposures on West Gull Lake, grows coarser toward 

 the center. This is one of the evidences in favor of the intrusive character 

 of the granite. In color the granite varies from light gray to pink, and 

 even to brick red. This last strong tint is usually present where the 

 alteration is the most pronounced. 



The granite massive is cut in vai'ious places by fine-grained red aplite 

 dikes. 



