232 GEOLOGICAL RECONNOISSANCE 



an extension of one and the same bed. Experience has shown that local 

 changes in the composition of the same vein of coal are not unusual, and 

 cannot alone be relied upon as a means of identification. The organic 

 remains of the roof shales and observations on the superposition of the 

 strata, are much surer guides in the determination of the position of beds 



of coal. 



For further remarks on the coals of Johnson county, see the Report of 

 Dr. D. D. Owen, State Geologist. 



East of Clarksville, and north of the Arkansas river bottoms, the heavy- 

 mass of dark shales, associated with the coal, disappear beneath the sur- 

 face, and the overlying sandstone becomes the surface rock, with some 

 intercalations of shale towards the base. The siliceous soil, derived 

 from this sandstone, supports a growth of large yellow pines, on the high 

 ridges between Clarksville and Dwight mission. 



Agriculture. 



The tillable up-lands of this county are derived principally from the 

 shales lying below the main mass of millstone grit rocks. Sample of 

 soils were collected for chemical examination, from Mr. Arthur Davis' 

 farm, one and a half miles east of Clarksville, where the growth was 

 principally postoak. 



The bottom lands, bordering on the Arkansas river, are highly esteemed 

 and very productive. 



POPE COUNTY. 



The geology of Pope county is almost a counterpart of that of Johnson. 

 The northern part is broken and mountainous. The mountains are com- 

 posed of massive sandstones, belonging to the millstone grit formation at 

 the summit, and thin-bedded and shaly sandstones at the base. Near the 

 head waters of Illinois bayou, the upper bed of sandstone is a true con- 

 glomerate charged with pebbles, huge blocks of which have rolled from 

 above into the valley beneath. 



On Indian creek, the subcarboniferous limestone appears beneath these 

 rocks, interstratified with reddish shales. This is the only limestone 

 observed in the county. 



South of Dover, between Illinois bayou and Galley creek, and south of 

 the Carrion Crow mountains, the country is comparatively level, where 

 the siliceous, red and dark argillaceous shales, having no capping of hard 



