EXCAVATION OF SMALL PITS. 329 



below. Although this lower marl also contains a large proportion 

 of clay, yet the carbonate of lime present, in finely-divided state, 

 not only preserves a very firm natural texture, but also prevents 

 adhesiveness in working ; unless the marl is permitted to receive 

 water after being dug and finely reduced. Then, indeed, it is made 

 a sticky mass; and the labour of shovelling it is more than doubled, 



The whole bed of marl at this place varies from 6 to 8 feet in 

 thickness, and generally is more than 7 feet, through the extent 

 of my work. The much larger part, of 4 to 6 feet thick, is per- 

 fectly impervious to the passage of water, though highly absorbent 

 of moisture, and always moist in its bed. This requires to be dug 

 by a heavy and narrow grubbing-hoe, which, in the hands of a good 

 pit-man, can be sunk barely 3 inches into this marl at a stroke. 

 Still lower, for a foot or more, the marl is softer, and the shells 

 are less reduced. And lowest, also for about a foot, the marl is in 

 large stony masses, lying so closely as to form a connected pavement. 

 The breaking up of this stony layer requires heavy and strong 

 picks, and the work is laborious and slow. But these hard lumps 

 are much richer in lime than the marl above. The excavation is 

 carried no deeper than through this stony layer ; and even that 

 has often been omitted, on account of the greater labour to dig, 

 and to throw it up from the greatest depth. 



Next below this stony layer is the green-sand earth, of great and 

 unknown depth. Here, this contains only about 2 or 3 per cent, 

 of carbonate of lime, in a few widely dispersed shells, with the 

 usual and considerable proportion of green-sand. I do not use this 

 etirth, nor deem it worth using as manure, where the upper marl 

 is to be obtained. Nevertheless, this lowest bed was formerly used 

 by the proprietor, and by others, in this neighbourhood, as "marl/ 7 

 without discrimination ; and it was then even preferred by most 

 persons to rich calcareous marl, if the latter were withaut green- 

 sand.* 



Excavation of Marl in small perpendicular pits. 



The first working was begun by digging and throwing off the 

 overlay adjoining a part of the narrow " out-crop" or exposed marl, 

 on the side of the natural gully through which the stream flowed, 

 so as to uncover a surface of marl 5 or 6 feet wide and 8 or 9 in 

 length (marked 1, in fig. 2). So narrow was the gully, and so lit- 

 tle fall had the stream, that it was difficult to dispose of the earth 

 from even this small uncovering. The marl was then dug out, so 



* The description of the strata is here generally confined to such features 

 as materially affected the labours of excavation, and removal of the overlay 

 and marl, or the supposed manuring values of the lower beds. In a subse- 

 quent part, in connexion with the marls of Virginia in general, the Pa- 

 munkey beds will be more fully described. 



