18 GEOLOGICAL REPORT. [131, 32 



Spirifer, Terebratula— and the pebble strata themselves are fre- 

 quently underlaid by a somewhat cellular breccia of angular frag- 

 ments of the same materials, which intervene between the pebble 

 strata and the unchanged carboniferous rocks. 



This breccia, which is usually cemented by a ferruginous material, sometimes 

 contains abundance of fossils ; though the hornstone in mass is poor in these, 

 and they are generally very poorly preserved ; oftentimes, indeed, it appears 

 as though the stratum had only been thoroughly shattered by some cause without 

 removing the fragments much from their natural position, so that those 

 belonging together have been re-cemented in loco ; the ferruginous cement, at 

 the same time, has penetrated the hornstone to the deptli of 1-10 to 1-8 of an 

 inch, so as to imbue completely the smaller fragments. This hornstone is ex- 

 ceedingly brittle, so as to fly to pieces readily whenever the surface even of a 

 large block is broken by the hammer. From semi-transparent, flinty varieties, 

 this rock sometimes passes through all gradations into an opaque and soft stone, 

 and finally into white, pulverulent silex, which forms a stratum of about 10 

 feet thickness in the neighborhood of Eastport, Tishomingo county. The soft 

 mass is at times traversed by harder layers, or bands of hornstone ; both in the 

 latter and in the pulverulent mass, carboniferous fossils are found, though 

 sparingly. 



31. On S. 16, T. 2 R. 10 E., near Scruggs' Bridge, in the same county, I observed 

 in a well, overlying the carboniferous limestone, ledges of this hornstone, two to 

 six inches in thickness, alternating with layers of about the same thickness, 

 composed of hoth pebbles and angular fragments of hornstone, imbedded in a 

 pale bluish clay. 



It is difficult indeed, under these circumstances, to determine definitely to 

 which formation the breccia and brittle hornstone strata properly belong. While 

 in some respects they closely resemble the rocks of the siliceous stage of the 

 Carboniferous, the intimate connection of a part of the hornstone at least, with 

 the pebble strata, seems equally obvious ; and the cement of the breccia at least 

 is most probably of Orange Sand age. Here, as elsewhere, the pebbles are totally 

 destitute of calcareous materials, which the Orange Sand appears to have in all 

 cases metamorphosed, or rather pseudomorphosed, by means of siliceous or 

 ferruginous solutions ; but we find frequently in the pebbles, an oolitic structure 

 which belongs to the carboniferous limestones of the region ; the material being, 

 however, entirely siliceous. Might not the same solution which effected this 

 pseudomorphosis, have been instrumental in forming the brittle hornstone and 

 breccia? 



32. I ought to mention in this connection, the singular change, resembling 

 decay, which purely siliceous pebbles of various kinds sometimes appear to have 

 undergone in particular regions. The most striking example I have seen occurs 

 in Simpson county, near Cokesville or Cokes School House, N. E. 1-4 T 10 R 17 

 W. Wells here are of great depth — 100 feet — and a few feet beneath the surface, 

 there appear beds of (generally small) pebbles mixed with yellow sand. The 



