ESDUCH.] GEOLOGY DISTRIBUTION OF GEANITE. 281 



pointing toward some small outcrops of it on Casto and Bates Hills. 

 North of the Winnebago mine, it crops -out ; also west of it, and east of 

 the Bates lode. How far it extends westward from the summit of Quartz 

 Hill, I am unable to say; probably not far, however. This is the extent 

 of the granite, and it will be found that within its limits, or in portions 

 immediately contiguous, the greater number of the lodes are located. 

 Porphyry crowns the top of Quartz Hill, Mammoth, Gregory, and Bob- 

 tail Hills, occurring besides in a dike on the western slope of Running 

 Hill, on Procer, and in a large dike north of Procer. Drawing a line 

 from the summit of Quartz Hill to that of Bobtail, it will be found to 

 run parallel with the main strike of the lodes, parallel with the longitu- 

 dinal axis of the granite — in other words, the porphyritic outflow has 

 a strike parallel to that of the granite, and both are parallel to that of 

 the lodes. 



Hornblende-rock occurs in dikes having an approximate strike of 

 north to south, composed of oligociase and hornblende, associated with 

 epidote and garnet. Several, from three to twenty feet in thickness, 

 cross Gunnell Hill, one extending across to Kansas Hill, and one crossing 

 Proper. Lithologically, the rock forming these dikes is diorite, although 

 it undergoes a series of modifications. 



On Plate II, a number of sections are given that will explain the rela- 

 tive position of the three formations occurring. Section A runs from 

 Quartz Hill to Eunning Hill, almost east 20° north. Chimneys of por- 

 phyry break through the grg^nite at four points along that section, 

 always forming the summits of small hills. Probably, without any 

 deep-reaching separation, the granite continues in narrow line for more 

 than three miles. Small patches of gneiss are found every now and then, 

 but are merely suiDerficial. As this section runs parallel to the strike of 

 the lodes, none are cut by it, with the exception of a small one on Eun- 

 ning Hill, that occurs out of course contact between porphyry and the 

 granite. Section B runs almost north 5° east from Gregory Hill to Bates 

 Hill, cutting the Mammoth, Gregory, Briggs, Bates, and Mack. Mam- 

 moth, and probably Gregory, as soon as it goes deeper, run in granite only, 

 while the remaining three are contact between gneiss and granite. 

 Section C shows the Mammoth on Mammoth Hill, where it has become 

 contact, whUe it is not farther east. Section D has a course from south 

 to north, running through Bobtail Hill, cutting the lode. Porphyry, sur- 

 rounded by granite, forms the top of the hill, while a portion of gneiss 

 comes in toward the north, and between this and the following granite 

 the Bobtail is contact. Section E runs from south to north, starting 

 from the eastern slope of Quartz Hill and continuing over across Gun- 

 nell, cutting in its course the Kansas, Whiting, and Gunnell. The Kan- 

 sas is contact between granite and gneiss, while the rest run entirely 

 in gneiss. 



On Procer Hill, the granite is of a light yellow to white color, coarse- 

 grained, with yellowish orthoclase, white quartz, and black mica, and 

 this character may be taken as a tyiDC. Throughout the district the 

 granite contains small crystals of magnetite, the largest of which are 

 found on Gunnell Hill, almost an inch in diameter. On this hill the 

 granite assumes a more gneissic structure, which it shows at no other 

 point to that extent. On Quartz Hill, and from there eastward to Eun- 

 ning, its character remains almost the same as well in mineral con- 

 stituents as in structure. Sometimes the line between it and the gneiss 

 is distinctly marked along the sides of gulches — particularly so on Kan- 

 sas Hill — but oftener it is obliterated. Slight variations of composition 

 are shown by the porphyry, which must be classed among the quartzose. 



