NOBTH-CAKOLIKA GEOLOGICAL SURVEY. 



have been spread out by some general cause, and at one 

 specific period. 



This bed, however, is not confined to this State. It extends 

 over a part of Maryland, Virginia, South Carolina, Georgia, 

 and Alabama. 



It is, therefore, a wide spread stratum, having its origin 

 through the influence of general causes. That this cause or 

 force operated with considerable violence is indicated by the 

 losses which one at least of the inferior formations has sus- 

 tained. The shell marl, for example, is never a continuous 

 deposit, and some of the beds are frequently furrowed and 

 channelled, apparently by a rush of water over them, remov- 

 ing not only the upper layers, but cutting frequently deep 

 into the beds. An erosion of this kind is illustrated by fig. 5. 

 The brown earth fills these eroded channels without mixing 

 at all with the marl. 



The next stratum beneath is a brick clay, which is also 

 general, but it is absent occasionally, in which case the brown 

 bed occupies its place. This clay varies considerably in com- 

 position ; it is sometimes charged with sand, in others it is 

 very fine and compact, and makes the best of brick. It 

 passes also into potter's clay. It is bluish white, gray and 

 reddish at different places. It never exceeds five feet in 

 thickness. 



4. The fourth stratum is sand, usually gray, and loose in 

 texture, not unlike quick sand. 



5. The shell marl occupies the fifth place in the descending 

 order. It wjll be fully described hereafter. 



6. The beds of green sand occupy the sixth place, and at 

 Blackrock it may be divided into two beds ; the upper con* 

 tains a large amount of clay, and the lower is sandy with 

 more lime ; it is also indurated, or partially consolidated. 



The lower mass forms a shelving projection from the upper, 

 some eight or ten feet wide, when it falls off perpendicularly 

 to a depth of fifteen fe^j.* The lower part is always under 

 water, and I know of 9b locality at which this part of the 

 formation is exposed. I regard this as an unfortunate circum- 

 stance, inasmuch as I have reason to believe that the quality 



