39 f 23 ] 



otherwise durable nature. They must also, to insure durability, be in all 

 cases laid on the bed as in the natural position in the quarry. 



The singular property which the best quality of these freestones pos- 

 sesses, of hardening by exposure, is one of its most valuable characteristics ; 

 permitting it to be wrought ai 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 composition, 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 hme, and acting as a ce- 

 ment 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 properly not yet suggested. 



This same property of hardening by exposure is possessed in a remark- 

 able degree by a building-stone which has been excavated for centuries 

 from St. Peter's mountain, in the vicinity of Maestrich, in Belgium, and 

 which is the terminating member of the cretaceous formation of the Mc- 

 sozoic period. This rock is a calcareous freestone, and is generally sup- 

 posed 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 lima. 



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

 to two letters which I addressed from Indiana, under date the 22d and 

 25th of October last, to one of your committee, (the Hon. VVm. 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 geo- 

 logical map in my possession, that the red sandstone formation which fur- 

 nishes highly-prized building-material in New Jersey and Pennsylvania 

 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 hberty 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 Washington, 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, m 

 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 

 Potomac 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 ex- 

 amination 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 OWEiN. 



Washington, March 15, 1847. 



