24 GEOLOGICAL REPORT. [142, 43, 44 



42. A much more common effect of the contact of the Orange 

 Sand with the Lignitic clays, is the appearance, on the line of 

 contact, of variously shaped nodules of aluminous brown iron ore, 

 of various degrees of purity not ouly in different localities, but 

 within one and the same nodule. These nodules are so common in 

 the eastern portion of the Northern Lignitic, from Tippah and E. 

 Marshall to Lauderdale county, that they become the habitual 

 surface indication of that formation, and are, therefore, very 

 frequently found associated with silicified wood. Their usual 

 shape is that of a flattened ellipsoid, and their size ranges from 

 that of a marble to a diameter of 2^, and even three feet in one 

 direction ; when of large size, they are ordinarily very much 

 flattened as well as lengthened. Being generally imbedded in clay, 

 their outside is usually quite smooth; internally, they consist of 

 concentric layers of different degrees of purity, which sometimes 

 inclose a core of pure brown hematite, but more commonly a maze 

 of cellular cavities, often resembling a honeycomb, either empty or 

 filled with yellow ochre more or less pure. In the " Hills of the 

 Flatwoods Region" (see Agricultural Report) they may frequently 

 be seen on the hillsides, mingled with the common ferruginous 

 sandstone (from the hilltops), from which, however, they are readily 

 distinguished by their peculiar structure, and the fineness of their 

 material. They serve as a very convenient mark of the level at 

 which the impervious clays occur, and to which, therefore, the 

 wells on the ridges will ordinarily require to be sunk. 



43. Sometimes, though on the whole but rarely, we find brown hematite 

 taking the place of silex in the petrification of wood ; and fragments of wood 

 thus ferruginized (of the same origin, no doubt, as the silicified wood) are 

 occasionally imbedded in the ferruginous sandstone of the hilltops. The 

 vegetable structure is in these cases but poorly preserved, so as to render it 

 difficult, if not impossible, to identify the species. 



44. The frequent occurrence of silicified wood, under the circumstances before 

 discussed, as well as the hard siliceous sandstones previously mentioned (if 15), 

 show that a liberal supply of soluble silex, has, in times past, been active in 

 many portions of the formation. That the hard and flinty trunks now found 

 were once in a soft or gelatinous condition, may be inferred from the fact that 

 few large trunks have remained entire, or if so, are solid inside. Usually, we 

 find them split up in billets, and when a round trunk occurs, a cross section 

 generally shows numerous crevices running out radially from a hollow centre — 

 Such as would result from contraction in drying. The silicified mass itself 

 exhibits all the several varieties ot amorphous quartz, from semi-transparent 



