[ 23 ] 36 



sition flagging at a future day ; or, what I would deem preferable, dispense 

 with the wood floor altogether at first, and raise the deafening above so as 

 to cover the floor-beams, upon which lay a floor of stone flagging. This 

 it is beHeved may be done at a small expense over the wood Mosaic, be 

 greatly more secure against fire, and require much less expense in clean- 

 ing and repairs. 



1 would also recommend as a security against fire, in case of the burning 

 of the roof, that a rough floor be laid upon the beams above the upper 

 ceiling, next to ihe roof, throughout the building, and covered with a suita- 

 ble thickness of lime-water cement ; over which, when dried, a covering of 

 common salt, or a cement of salt and ashes, be evenly spread, carefully 

 filling all the cracks or crevices of the cement. 



This is the French method of fire- proofing the upper part of build- 

 ino^s, and has been to some extent adopted in some sections of this coun- 

 try with entire success. This would be attended with comparatively little 

 expense, and would, it is believed, render the body of the building en- 

 tirely secure against destruction by fire incase the roof should be burnt. 



All of which is respectfully submitted. 



WM. J. HOUGH. 



Washington, March 15, 1847. 



On motion of Mr. Seaton, it was 



Resolved, That Mr. Hough be requested to examine into the expedi- 

 ency of dispensing with any portion of ornamental stucco in the build- 

 ing. 



The chairman submitted from Dr. Owen the following 



Report on the sandstmies of the Potomac. 



After completing the report of the white marbles and granite of Balti- 

 more county, Maryland, I proceeded, according to instructions, on the 

 afternoon of the ilth of March, to inspect the quarries of sandstone in 

 the neighborhood of Seneca creek, Montgomery county, Maryland. 



About 2\.\ miles from Washington city, on the line of the Chesapeake 

 and Ohio canal, the talcose and chloritic schists of the Great falls of the 

 Potomac are succeeded by freestone and marly beds of the new red sand- 

 stone forination. These deposites are of various colors, from a light 

 greenish-gray, or dove-color, to a deep red or brown. 



Tne first quarry visited is situated on Bull run, 23 miles from Wash- 

 ington. The excavations have hitherto been carried on from 250 to 300 

 yards on the north side of the canal ; but the ledges of rock extend down 

 to its margin, and can be quarried with nearly as much laciiity a few 

 paces from the canal as where operations are now carried on. 



The dip of the stratification slopes at an angle of 15° or 20*^ up- 

 wards from Bull run. The beds, suitable, both as regards color, durabili- 

 ty, and ease with which they can be cut, are fortunately near the surface 

 in the ravine ot Bull run. By commencing quarrying operations near 

 the bed of this stream, and working up the western slope, blocks of large 

 dimensions can be obtained with comparatively little labor. The beds 

 whicti have been chiefly worked here are layers of a deep red color, (see 

 specimen No. 18,) and layers of a purplish-gray, (No. 19,) which, by expo- 

 sure, acquire a lighter and more pinky hue. The latter is the rock most 



