1S97.] l^RAKE — THE GEOLOGY OF IXDIAX TERRITORY. 341 



Chetnical Analysis.^ — per cent. 



Loss on Ignition i.ii 



Silica (SiOo) 71.10 



Ferric Oxide and Alumina (Fe.^ O3 and AI2O3) 20.60 



Calcium Oxide (CaO) 2.53 



Magnesium Oxide (MgO) 0.99 



Potassium and Sodium Oxide (K2O and Na.^0) 3.76 



Total 100.09 



Classification of the Rock. — The high percentage of silica, the 

 holocrystalline texture and the general interference of crystallization 

 shown in the irregular crystal outlines at once place the rock in 

 the granitic series. As shown by the feldspars, quartz and mag- 

 netite, however, there is a strong tendency to the porphyritic texture: 

 it is, therefore, a porphyritic granite. The minute textures of the 

 feldspars and quartz is designated by the name granophyre. 



Age of the Dike. — As noted above, the dike breaks through 

 Silurian strata along the axis of an anticlinal fold. The Lower Car- 

 boniferous strata overlying the Silurian are tilted by this fold. The 

 igneous rock was, from this evidence, most likely protruded at the 

 time of the folding. This anticline is one of the outlying folds of 

 that mountain system which is such a marked feature of central 

 western Arkansas and the adjoining part of the Indian Territory. 

 This system of folding is post-Carboniferous, pre- Cretaceous and 

 quite likely pre-Mesozoic, because Upper Coal Measures deposits are 

 folded. Lower Cretaceous deposits lie almost undisturbed upon these 

 folds and no Jurassic or Triassic beds occur over the area. 



Relatio7i to the Igneous Rocks of Other Areas. — This dike in 

 the Cherokee Nation is equally distant from three different igneous 

 rock areas, and about two hundred miles from either of them. One 

 lies in southeastern Missouri, one in central Arkansas and the other 

 in the Choctaw and Chickasaw Nations, Indian Territory. The 

 igneous rocks of this latter-named area have not been studied by 

 any one sufficiently to make satisfactory comparisons. The igneous 

 rocks of Arkansas are quite different from the Spavinaw granite. 

 Those of Arkansas " belong to the eleolite syenites and their asso- 

 ciated dike rocks ;" they are gray or blue in color- and are post-Car- 



1 Analysis made by Mr. Chester A. Thomas. 

 "^ Anil. Rept. Geo I. Surv. Ark.^ 1890, Vol. ii, p. 3. 

 PROC. AMER. PHILOS. 800. XXXYI. 156. X. PRINTED DEC. 17, 189T. 



