37 [ 23 ] 



suitable for building purposes, its color being agreeable, and, in the opin- 

 ion of men of good judgment and taste, appropriate for the Norman style 

 of architecture. Tliis rock possesses one property in particular which 

 recommends it to the attention of builders. When first removed tiom 

 the parent bed, it is comparatively soft, working freely before the chisel 

 and hammer, and can even be cut with a knife: by exposure, it gradually 

 indurates, and ultimately acquires a toughness and consistency that not 

 only enables it to resist atmospheric vicissitudes, but even the most severe 

 mechanical wear and tear. Abundant evidence of this is afforded in the 

 buildings of the neighborhood, in several of the locks and aqueducts, and 

 also in ledges and blocks exposed in the bed of Bull run. The deep red 

 varieties have been chiefly used in these structures. By close inspection 

 of slabs exposed now 20 years to atmospheric agencies and severe me- 

 chanical friction, the mark of the dressing-chisel is still sharply imprint- 

 ed in the surface. On the perpendicular wall of the aqueduct, where the 

 water has been oozing through the joints and trickling down its face, 

 forming an incrustation of carbonate of lime, one may observe, where 

 this calcareous crust has scaled off, the grooves and ridges of the surface 

 still nearly as distinct as when the block first came from the hand of the 

 stonecutter. 



The angles and edges of the keystones of the arch, placed under these 

 most unfavorable circumstances, are sharp and entire. Only one or two 

 blocks of this work of 20 years' standing show signs of decay; but these 

 seem to be such as either have not been well selected, or have been 

 placed on the edge in the wall. 



Even the tow-path of this aqueduct, over which the horses and mules 

 have been travelling for 20 years, is still unimpaired. Even the corners 

 around which the heavy lock-gates swing, show no signs of chipping. 

 Blocks were pointed out to me in the bed of Bull run, which had been 

 rejected by the engineers as being of too soft and perishable a nature, and 

 which have been exposed for 20 years to the action of running water and 

 alternate thawing and freezing, which exhibit little or no alteration, ex- 

 cept that they have become so indurated that. they turn the edge of the 

 chisel, and are a little dingy on the surface. 



Mr. Peter, on whose property this quarry is situated, has built a fine 

 barn of these freestones. He assures me that there are stones in that 

 barn 50 years old, which have been in three buildings. On one corner- 

 stone, where the figures " 1824" had been cut in that year by the point of 

 a jienknife, the rock now is so hard that it would soon turn the edge of 

 a well-tempered tool. 



Interstratified with these grit-stones are some argillaceous, marly-look- 

 ing beds, (No. 20,) especially prevalent towards the upper outcrop of the 

 stratified mass constituting these hills. These layers are, of course, ennre- 

 ly unfit for any kind of building purposes. The sandstone beds differ 

 very much, not only in color, but also in hardness and texture. Some 

 are fine-grained, and can be wrought to a sharp arris ; others are coarse- 

 grained, and even assume the character of a conglomerate: these latter, of 

 course, are entirely unfit for the finer purposes of architecture. Amongst 

 a series varying so much, not only in color, but in texture and composi- 

 tioM, a careful selection becomes a matter of the utmost importance. 



About a quarter of a mile further west, in a bold escarpment oi 20 or 

 30 feet in height, close to the margin of the canal, is the " College quar- 



