338 DRAKE — Till-: (tEOLOGY of IXDIAX territory. [Sept. 3, 



Igneous Rocks. 



Previous Kno'cvlcdge of the Igneous Rock. — The existence of 

 igneous rock in the Cherokee Nation has been known for a long 

 time. It was referred to in D. D. Owen's Second Report of the 

 Geology of Arkansas as a red granite which occurred at the mouth 

 of Spavinaw creek, some thirty or forty miles west of the Arkansas 

 line. Edward T. Cox failed to find the granite in place, but saw 

 some millstones that were made from it, and obtained specimens 

 which were broken off in fashioning the millstones. He thought 

 this granite underlay the sedimentary rocks of southwestern Mis- 

 souri and northwestern Arkansas.^ 



The exact locality of this granite outcrop has, however, appa- 

 rently never been definitely known to any one interested in the 

 geology of the country until 1896, when the writer, after a special 

 search, found the rock in place. 



Locality and Mode of Occurrence. — The rock occurs in the Cher- 

 okee Nation, on the north side of Spavinaw creek, about six miles 

 from its mouth and three-fourths of a mile west of Spavinaw post- 

 office. It is a dike about twelve hundred feet long by fifty feet 

 wide. The outcrop is not continuously exposed, but the breaks are 

 probably due to a thin covering of detritus from the clastic rock. 

 There are four exposures of the dike rock, which vary in length 

 from about one hundred to two hundred feet, and occur at inter- 

 vals of about two hundred feet. 



This dike runs along the axis of a gentle anticlinal fold which 

 extends about N. 30^ E. The dips of the sedimentary beds on 

 either side of the dike are only 5° to 10°, but the fold is broad and 

 affects the rocks for two to three miles to the west and probably as 

 far to the east. Silurian strata which, over the adjoining country, 

 are usually covered by two hundred to five hundred feet of Lower 

 Carboniferous beds, are here exposed to a depth of about two hun- 

 dred feet and outcrop in the valley, as shown in PL III. The Silu- 

 rian strata along the contact of the dike appear to be free from any 

 special metamorphic action due to the dike rock. 



Macroscopic Characters. — The general color of the rock is a 

 light brick red with a mingling of black specks which are slightly 

 grouped and in places so much as to give it a somewhat 



'^Second Report of a Geological Reconnaissance of the Middle and Southern 

 Comities of Arkansas^ lSo9 and 18G0, pp. 404, 408. 

 '^Ibid., p, 40S. 



