202 THE MINERAL RESOURCES OE CECIL COUNTY 



Maryland building stones were studied, among which was included 

 the Port Deposit granite. Dr. Chas. G. Page, in his report on the 

 action of frost on certain materials for building, gives as the specific 

 gravity for the Port Deposit the figures 2.609, and as the loss by frost 

 in grains 5.05. The method of investigation was the so-called Brard 

 process, which consists in substituting the crystallization of sulphate 

 of soda for the freezing of water. 



The tests published in the second volume of the Maryland Geo- 

 logical Survey Reports are even more creditable to the rock. The 

 specimens submitted were two inch cubes, carefully prepared and 

 subjected to tests under the most uniform conditions. The results 

 are as follows: 



Simple Crushing. Absorption, Freezing 1 , Crushing after freezing. 



, * > percentage percentage / " « 



Crack. Break. of gain. of loss. Crack. Break. 



67,100 0.253 0.000 83,000 86,000 



79,200 0.193 0.011 78,100 90,800 



86,200 



101,540 



Tests made by Messrs. Booth, Garrett, and Blair, of Philadelphia, 

 on a 2-inch cube gave the crushing strength as 84,730 pounds for 

 2-inch cubes. 1 



The results of these various investigations clearly show that the 

 Port Deposit rock is strong enough to withstand all the demands made 

 upon it by the pressure of superimposed stone work in structures, 

 and to resist the various deteriorating influences of frost and atmos- 

 phere. 



This view of the durability of the Port Deposit granite is well sus- 

 tained by a study of its mineral ogical and chemical composition, and 

 the evidence of disintegration shown in the quarries and in old struc- 

 tures. The mineral ogical composition indicates stability, as no min- 

 eral is present more liable to alteration than the oligoelase feldspar, 

 which itself is not particularly prone to decomposition, although the 

 first of the prominent constituents to yield to atmospheric action. In- 

 vestigation at the quarries, where a considerable depth of decomposed 

 rock is seen to overlie the more marketable material suggests the sus- 



18th Ann. Rept. U. S. Geol. Surv., pt. V, 1897, p. 964. 



