16 GEOLOGICAL REPORT. [1F27 



27. The instance in question occurs in the deep cut on the Memphis and 

 Charleston llailroad, afeout 4 miles east of Pocahontas Station, in Tennessee, 

 but deserves description here on account of its importance in a geological point of 



.view. 



[No. 1.] 



s s s. Loose yellow sand. 



III. Indurate ledges (ferruginous sandstone.) 



c. Mass of black clay 



The cut in cpuestion (Diagram No. 1.) is ninety feet deep, through a ridge 

 dividing the Tuscumbia river from one of its eastern confluents. The main 

 body of the ridge consists of yellow and orange colored sands (with occasional 

 layers of pipeclay) in which, fortunately for the permanence of the excavation, 

 there are several successive indurate ledges, (J 1 1,) ferruginized, which serve as 

 shelves to support the caving sand. On the western half of the cut, there lies 

 imbedded in the sand, and surrounded by it as far as visible, a basin shaped 

 mass of black, tenacious, fetid clay, (c,) with scarcely a trace of stratification, 

 At the center of the basin, about 15 feet of this mass are visible above the road- 

 bed ; its total thickness, as indicated by the visible part of the outline would be 

 about twenty feet, with a maximum length of 75 yards. The clay contains, 

 diffused throughout the mass, minute crystals of iron pyrites and a few very 

 indistinct', carbonized remains of plants, apparently grasses, and perhaps, 

 willows. On the outside and upper surface of the mass, however, there is a shell 

 as it were, of cream colored clay, one to four inches in thickness ; evidently the 

 same as the rest, and passing into it by a shaded band of transition. The same 

 cream color is assumed by the black clay when it is burnt, and in the present 

 case it is evidently the result of oxidation from the outside. [Similar cream 

 colored clays are very common elsewhere in the Orange Sand formation.] The 

 stratification lines of the surrounding sands, which elsewhere exhibit the usual 

 wavy appearance, show a decided inflection downwards, and the layers thin out 

 as they approach the mass, so as to conform, to a considerable extent, to its 

 external shape. 



Special descriptions of some of the more notable deposits of 

 clays in the Orange Sands will be found under the head of the 

 Useful Materials of this formation. 



