312 GEOLOGICAL SURVEY OF THE TERRITOEIES. 



tion or as the oldest Carboniferous, which I prefer m this instance for 

 stratigrapbical reasons. Bluish shales (m) that have been eroded con- 

 siderably follow, forming the bottom of a narrow valley, and are covered 

 in turn by a gray saccharoidal limestone {n) rising steeply from them. 

 A gentle dip, about 7° to 10°,' pervades throughout, gradually lessening 

 toward the northeast. Proceeding onward in that direction, the red 

 sandstone, which has not appeared for four or five miles along the line 

 of Carboniferous outcrop, is again found, forming bluffs of the classical 

 "hog-back " shape. On the summits of these low bluffs innumerable 

 fragments of yellow, red, and brown jasper were found, a circumstance 

 which I have observed in several instances in the same formation, 

 although many miles distant, thus affording x>robably a slight hint for 

 the parallelization of strata. Following along the section-line, a small 

 quantity of rhyolite is found to have overflowed this red sandstone, (e.) 

 It appears again, however, probably owing to erosion, about three-quar- 

 ters of a mile farther on, (e.) The rhyolitic bluff in question is about 

 80 to 100 feet high, weathering in grotesque forms. Andesitic tuffs and 

 rhyolite again cover the sandstone, so that the line of junction can be 

 traced for several hundred yards. A slight folding seems to take place 

 at this second exposure of the sandstone, possibly owing its formation 

 to the lateral pressure coming from north and northeast during the 

 period of massive volcanic eruptions. To facilitate the ready compre- 

 hension, both of locality and distribution of the formation, a diagram 

 has been prepared, the dotted line indicating the course of the sec- 

 tion. 



South of the points just under consideration, the Carboniferous again 

 follows the Silurian in a very narrow strip, on its sudden turn, until 

 it reaches a locality about five miles east of station 57', where it sud- 

 denly widens out, covering a comparatively large area of land. Of the 

 lower limestones, a ijortion follow along the Silurian, conformably over- 

 lying it, and are in turn covered by the red sandstone mentioned above. 

 An immense development of vertical dimensions is attained by this sand- 

 stone, which covers an area of more than twenty -five square miles, and 

 dips at an angle of 15° to 17° to the northeast. In respect to strati- 

 graphical conditions as well as lithological character, its strata present 

 a very uniform appearance. Taking the thickness of the combined 

 strata, it amounts to more than 5,000 feet, while the development in 

 section b seems to be still greater. To this sandstone, characteristic not 

 only as an excellent geoguostic horizon, I give the name of Arkansas 

 sandstone, from its proximity to that river. Running parallel with the 

 main direction of the formation just spoken of, is a spur of Carbonif- 

 erous limestones, west of stations 60 and 01, separated from the remain- 

 der by a strip of granite. A well-marked line of sharp bluffs, the strata 

 of which dip steeply to the eastward, faces the western border of this spur. 

 Favosites and a few other fossils that were found afford no reliable clew 

 to their position, but for stratigrapbical reasons it must bo considered as 

 properly belonging above the Arkansas sandstone. Gray and bluish 

 limestones compose the entire mass. 



As a rule, the Carboniferous beds form, a continuation of the grassy or 

 wooded slopes initiated by the Silurian; and having suffered but little, 

 scarcely at all, from disturbances of various kinds, usually present 

 gentle outlines, varied, however, by the more sterile sandstone areas. 

 Possessing a dark-red color and singular uniformity in features, the lat- 

 ter make a less i)leasant impression than the timbered limestone hills 

 inclosing well-waterd valleys. 



Between the formation last spoken of and the next one fo^^owiug, a 

 wide gap occurs in the adopted succession of geological epochs. Next 



