1S07.] DRAKE — THE GEOLOGY OF INDIAN TERRITORY. 343 



Local Develop/neni. — The localities where the writer saw and ex- 

 amined Silurian deposits are on Spavinaw creek six to seven miles 

 from its mouth, along the Illinois river southeast of Oaks, along 

 Salisaw creek at and near Marble and on Elk creek west of Bunch. 



Spavinaw Creek Area. — The area on Spavinaw creek is shown in 

 PL III. It is about one mile square, and is exposed mainly on ac- 

 count of an anticlinal fold which elevates the beds so that the 

 erosion of Spavinaw creek has reached and cut into them. About 

 two hundred feet of the strata are exposed. The rocks are mainly 

 cherty limestones, cherty calcareous sandstones and saccharoidal 

 sandstones. The lowest exposed strata lie practically in contact with 

 the igneous dike and are composed of fossiliferous chert. Along the 

 creek at Spavinaw post-office twenty feet or more of the Silurian 

 strata are exposed. 



Illinois River Areas. — At the Stewie ford of the Illinois river on 

 the Cincinnati-Oaks road, about seventy-five to one hundred feet 

 of Silurian strata are exposed in the bluffs and the hillsides along 

 the valley. These strata are mainly saccharoidal sandstones, rather 

 thin bedded, but sandy clay shale is quite frequently interstratified 

 with the sandstone. These clays are of a light gray color and in 

 places are slightly blue, and some are yellowish. Silurian strata 

 are exposed on the above-named road also about two miles to the 

 northwest of the ford, at which exposure the beds are saccharoidal 

 sandstones dipping slightly to the southeast. Good exposures of 

 the thin bedded sandstone and shales may be seen at the Stewie 

 schoolhouse about one-half mile northwest of the ford. From the 

 exposures seen along and near the river, it seems likely that the 

 outcrops extend several miles up and down the valley from the foid. 

 Silurian strata are reached by this river erosion along the Arkansas- 

 Indian Territory line, and they are nearly reached in the bed of 

 the river east of Greenleaf courthouse, some twelve to fifteen miles 

 southeast of Tahlequah. So it is probable that exposures may be 

 seen for twenty or thirty miles along the river valley within the 

 Cherokee Nation. 



Salisaw Creek Areas. — The exposures of Silurian deposits on 

 Salisaw creek were caused by folding, faulting and erosion. The 

 location and areal outcrop of these beds are shown in PI. IV. The 

 Silurian strata nowhere rise high upon the hillsides, but are almost 

 entirely confined to the deeper erosion channels of the valleys and 

 canons. They are exposed, however, only where folding or fault- 



