108 NORTH-CAROLINA GEOLOGICAL SURVEY. 



absence is due to denudation, or whether the beds were 

 formed only at certain points, has not been determined. De- 

 nudation, however, has taken place at some of the beds, as 

 they still preserve the gullies which were cut through them, 

 and which were subsequently filled with brown earth. 



Although it is not possible to detect an orderly arrange- 

 ment of materials, still, certain parts occupy usually a com- 

 mon position ; for instance, the large pebbles, coprolites-, and 

 certain bones and teeth lie at the bottom of the stratum. 

 The inference which may be deduced from this fact is, that 

 during the first stage of its formation, there was considerable 

 violence in the movement of the waters in which the stratum 

 was accumulating ; and that probably, prior to, and during 

 the early part of its accumulation, there were shiftings of the 

 strata; some being more elevated, others depressed; or there 

 was a change of level of the sea coast, which set in motion 

 the waters, and led to the violence which collected at the 

 bottom the large and less destructible fragments to which I 

 have alluded. 



But in the first place, I propose to speak of the use of this 

 marl stratum as a fertilizer ; and as it has a more general dis- 

 tribution, it has been employed more extensively than either 

 of the foregoing which I have described. 



The beds of shell marl are not composed uniformly of the 

 same elements in the same proportions. It is as heteroge- 

 neous as possible in this respect. Some beds contain ninety 

 per cent of sand ; in others it is reduced to twenty-five per 

 cent, and the remainder is mostly carbonate of lime. 



79. The most important subdivision which can be found- 

 ed upon composition, is that into a gray or whitish marl in 

 the mass, the color of which is due to the great abundance 

 of marine shells, and that of a dark bluish green marl, which 

 contains grains of green sand. In the latter there is a no- 

 table amount of potash, while in the former it exists only in 

 very small proportions. Some recognize a red or brown 

 marl. This color, however, is due merely to exposure to the 

 atmosphere, in consequence of which the protoxide of iron 

 has changed, or is changing, by the absorption of oxygen 



