POTOMAC AND KAPPAHANNOC. 291 



Under the rock fine loose sand. 



In this rock, winch runs N. E. and S. W. there is no joint 

 horizontal or perpendicular, and columns of any size, not ex- 

 ceeding 15 feet diameter, might he got out of it, it they could 

 afterwards be removed. — The largest blocks however which I 

 have had taken out, do not exceed in weight four tons. 



In working these quarries, the workmen having cut the face 

 perpendicularly, first undermine the rock; — an easy operation, 

 the substratum being loose sand. If the block is intended to 

 be 8 feet thick, they undermine it 5 feet, in a horizontal di- 

 rection, in order that it may fall over when cut off. They 

 then cut two perpendicular channels on each hand, 1ft. 6in. 

 wide, at the distance from each other of the length of their 

 block, having then removed the earth and rubbish from a ditch 

 or channel along the top of the rock, they cut into the rock 

 itself, a groove, and put in wedges along its whole length. 

 These wedges are successively driven, the rock cracks very re- 

 gularly from top to bottom, and it falls over, brought down 

 partly by its own weight. Blocks have been thus quarried 40 

 feet long, 15 feet high, and 6 feet thick. The block which 

 was quarried at my last visit to the quarry, was of the follow- 

 ing dimensions: — 



26 feet long, x 8 feet deep, x 14 feet high = 2912 feet, 

 which at 15 feet to the ton, agreeably to the quarry rate, amounts 

 to near 200 tons. — These masses are then cut by wedges into 

 the sizes required. 



On referring to my memoir on the sand hills of cape Henry, 

 it will be seen that the sand is blown up from the margin of 

 the sea, inland; — that it soon forms a ridge or down of shifting 

 sand, along the shore above high water mark, covering the old 

 surface of the earth with all its vegetation, that in the course 

 of no very great length of time, it accumulates into hills that 

 destroy and swallow up forests in their progress; that its sur- 

 face is constantly changing with the operation of the wind : — 

 and that, therefore, this sand mass, must contain broken 

 limbs and bodies of trees, iron in greater or less quantity, 

 together with all kinds of extraneous matters, blown up from 



