﻿200 



NEW YORK STATE MUSEUM 



mu 



xxictltiplied by the specific gravity of the rock is then divided by the 

 above computed -weight of the poreless specimen. This ratio ex- 

 pressed as a percentage is the actual porosity. Expressed as a 

 formula, the computation is as follows : 



(Saturated wt. — Dry wt.) S. G. 



(Saturated wt. — Dry wt.) S. G. + Dry weight 



Porosity." 



3 Ratio of drying. An attempt has been made to determine the 

 comparative and actual rates at which the saturated rocks give up 

 the absorbed water under ordinary atmospheric conditions. " The 

 ratio of drying was computed by dividing the weight of water 

 lost during exposure by total weight absorbed. The weight of re- 

 tained water was computed." The comparison is most useful in 

 rocks of like petrographic general character. 



The other terms need no explanation. 



TABULATION OF TESTS 



Name 



a 



a 







6 

 53 



fi 



en <u 



4J 

 U (L> 



a 

 >. 





 u 

 O 

 Oh 



u 



m 



a 



CO 







O 



a> 



M 



id 

 %° 



u 

 u 



P4 



Ratio of 

 drying 



Retained water 

 pounds per 

 cubic feet 





24 



hours 



48 

 hours 



24 

 hours 



48 

 hours 



Granite, Ferris 

 quarry, core No. 461 



1 

 2 



0.34 

 0.31 



O.77 

 O.84 



2.66 

 2 .65 



164.7 \ 

 164.O j 



. 26 



49-45 



52.8 



. 224 



. 210 



Gneissoid granite, 

 Ferris quarry, 

 core No. 468 



1 

 2 



0.32 

 . 25 



O.81 

 O.71 



2.63 

 2 .65 



l6l .O ] 

 162.8 J 



0.28 



67.48 



69.88 



. 146 



.145 



Yonkers gneiss, 

 Dinnan quarry 



1 

 2 



0.30 

 0.39 



O.87 

 I .OI 



2 .64 

 2 .64 



163.3 1 

 161 .O j 



0.30 



88.16 



88.16 



• 057 



.057 



Dioritic gneiss, 

 Garden quarry, 

 core No. 459 



1 

 2 



.42 

 0. 24 



O.68 

 O.68 



2.83 

 2.86 



175-4 ■ 

 174.8 J 



0.21 



62 .5 



62 . 5 



• 137 



• 137 



Gneissoid granite, 

 Ferris quarry, 

 surface 



1 

 2 



0.37 

 0.98 



O. 96 



2 . SO 



2 .63 

 2 . 62 



162.5 1 

 159-4 J 



1.08 



86.7 



88.2 



.252 



.215 



Granite, Ferris 

 quarry, surface 



1 

 2 



0.44 

 . 19 



I . 12 

 O.50 



2 .63 

 2.71 



162.3 1 

 167.3 J 



.40 



70 .0 



74-0 



.207 



.180 



Mr Davis concludes from a careful analysis and interpretation of 

 these tests that the Yonkers gneiss is of superior durability. 



