614 REPORTS OF THE BUILDING COMMITTEE. 



The singular property which the hest quality of these freestones possesses, of hard- 

 ening by exposure, is one of its most valuable characteristics ; permitting it to be 

 •wrought at less expense than marble, and imparting to it a durability which increases 

 with age. It has been a question, whether this property is due to iron in its compo- 

 sition, passing from a lower to a higher degree of oxidation, or to the presence of a 

 sub-carbonate of lime, becoming gradually by exposure a carbonate of lime, and act- 

 ing as a cement to the particles of silex. A minute chemical analysis would, no 

 doubt, throw light on this matter. It might prove that this phenomenon depends on 

 some other property not yet suggested. 



This same property of hardening, by exposure, is possessed in a remarkable degree 

 by a building stone which has been excavated for centuries from St. Peter's Moun- 

 tain, in the vicinity of Maestrich, in Belgium, and which is the terminating member 

 of the cretaceous formation of the Mesozoic period. This rock is a calcareous free- 

 stone, and is generally supposed to owe its hardening property to a chemical change 

 which takes place in the calcareous cement. The Seneca freestone, however, does not 

 effervesce in mass with acid ; and this fact militates against the idea of its indurating 

 property being due to any peculiar form of carbonate of lime. 



In concluding this report, it may not be out of place briefly to advert to two let- 

 ters which I addressed from Indiana, under date the 22d and 25th of October last, to 

 one of your commitee, (the Hon. Wm. J. Hough,) on the subject of the sandstones 

 of the Potomac, which, at that time, I had not seen. In these letters, (judging from 

 the fact shown from a geological map in my possession, that the red sandstone forma- 

 tion which furnishes highly-prized building material in New Jersey and Pennsyl- 

 vania passes thence to the southward, and crosses the Potomac at Noland's Ferry, 

 descending that river on the Maryland side and crossing Monocacy and Seneca 

 creeks,) I took the liberty of suggesting the importance of a careful examination of 

 these localities, before selection was made of a more distant and expensive building 

 material. Mr. Hough will recollect that the second of these letters contains the 

 following paragraph : 



" It seems indeed strange, that, if really good and durable freestones are to be had 

 on the canal or river above Wasbington, these should not already have been used for 

 the public edifices there ; but sufficient examples are to be found of the very best 

 building material, having been overlooked through a long series of years, even in the 

 vicinity of populous cities, for lack of minute and discriminating examination. My 

 own firm belief is, that a durable sandstone, equal or nearly equal to that used in 

 Trinity church, can be discovered in sufficient (Quantities in the vicinity of the Poto- 

 mac or the canal." 



It may afford some evidence of the confidence with which geological science may 

 be appealed to in search of practical results, that an actual examination of one of 

 the localities above designated has fully confirmed all, and more than all, I had 

 anticipated, concerning the material they furnish. 



I annex a rough sketch of the College and Bull Run quarries, showing the dip of 

 the strata and the shape of the escarpments along the bank of the canal, where the 

 freestone is found. 



All which is respectfully submitted. 



DAVID DALE OWEN. 



Washington, March 15, 1847. 



List of Specimens referred to in the foregoing Report. 



18. Bed Potomac sandstone, Bull Run, near Seneca creek, Montgomery county, 



Maryland. 



19. Grayish-purple or pink variety of sandstone, Bull Eun, near Seneca creek, 



Montgomery county, Maryland. 



20. Disintegrating argillaceous beds, College quarry, west of Bull Bun, Montgom- 



ery county, Maryland. 



21. Dove-colored bed, College quarry, west of Bull Bun, Montgomery county, 



Maryland. 

 21a. Banded variety of 21. 



22. Purple and brown beds, No. 21, College quarry, west of Bull Eun, Montgom- 



ery county, Maryland. 



And, on motion, the committee adjourned. 



Eighth Meeting, March 16, 1847. 



Present, Messrs. Seaton, Hough, and Owen. 



The chairman laid before the committee the following letter : 



