172 ANNALS NEW YORK ACADEMY OF SCIENCES 



Mineralogy 



A crystallographic study and discussion of the minerals found within 

 the boundaries of this formation has already been published by the 

 writer;-' it serves as a summary of those species which, to the writer^s 

 knowledge, have been found in this region, up to the spring of 1912. 

 This description applies particularly to the deposits lying between Prince- 

 ton and the Delaware Eiver. 



Most of the best exposures, where minerals are obtainable, are in quar- 

 ries now being operated, where the continued accessibility of these de- 

 posits is well assured, and new occurrences are almost certain to appear^ 

 Most of the productive deposits are in seams 'carrying analcite, but many 

 of the calcite seams also will be found to be interesting. 



Commercial Aspects 



Some criteria for testing a rock in order to determine its availability 

 for building material are given by Dr. Chas. P. Berkey in his report on 

 the Catskill Aqueduct (p. 199). Among these are the following: 



Specific gravity. 

 Weight per cubic foot. 

 Porosity, in per cent. 

 Per cent water absorbed. 



The tests here enumerated were tried upon samples of the Lockatong^ 

 argillites, with the following results : 



The specific gravity of a specimen of the argillite from Princeton was 

 found to be 2.57. Hence the weight per cubic foot of the Princeton ma- 

 terial is 160.62 pounds. This agrees closely with the estimate of a con- 

 tractor using this stone in Princeton, and also witli the weights of many 

 standard building stones in use at the present day. 



A specimen of the hard reddish brown argillite from Matthews^s 

 quarry, Princeton, was ground to a nearly cubic shape, with smooth faces 

 about an inch square. This block was dried for 6 hours in an air bath at 

 a temperature of 130° Centigrade. It was then removed, and immersed 

 in a beaker of distilled water, in which it was boiled for half an hour^ 

 until no more air bubbles appeared on its surface. The surface of the 

 block was then dried off quickly, and upon weighing the sample was 

 found to have taken up .0014 per cent of its weight of water. This test 

 shows that the pore space of the argillite is exceedingly small, and that 

 the penetration of water into the rock is slight. The latter fact is well 



2^Amer. .Tour. Sci.. 4th series, Vol. XXXV, pp. 446-450. 191.3. 



