92 



GEOLOGICAL RECONNOISSANCE 



SECTION OF BOAT MOUNTAIN— Continued. 



d 



CD 



160 



I L | 

 L | I 



Sandstone of the millstone grit series, two 

 hundred feet in thickness — Continued. 



Upper yellowish subcarboniferous limestone, 

 including the Archimedes and encrinital 

 limestones, with alternations of shale ; one 

 hundred and sixty feet in thickness. 



stones are underlaid by 

 sixty feet of sandstone, 

 which repose on the 

 black bituminous shales 

 with calcareous and fer- 

 ruginous segregations 

 and septaria, which oc- 

 cupy a space along the 

 slope of the base of the 

 mountain, of sixty or 

 seventy feet. The cor- 

 rection for dip will, how- 

 ever, probably reduce its 

 actual thickness to forty 

 or fifty feet. This black 

 shale reposes on the 

 light-grey cherty lime- 

 stone, that constitutes 

 the base rock of Mar- 

 shall's prairie, which is 

 probably referrible to the 

 subcarboniferous era, be- 

 ing a part of the cherty 

 limestone group overly- 

 ing the marble limestone 

 on Cave creek, and else- 

 where, in Newton and 

 Searcy counties. It is 

 probable, that all the high 

 ranges of hills, constitu- 

 ting the Boston mountain 

 range of Newton county, 

 have a geological struc- 

 ture analogous to the 

 section here presented of 

 the Boat mountain, with, 

 probably, some local va- 

 riations in the relative 

 thickness of the differ- 

 ent members; since, in 





