200 



NEW YORK STATE MUSEUM 



multiplied 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 

 '% 



a 



w 



0* 



^ u 



©a 



1 



1 



M 

 '0 

 (XI 







1 



ti 



Ratio of 

 drying 



Retainec 

 pound 

 cubic 



water 

 sper 



feet 





24 

 hours 



48 

 hours 



24 

 hours 



48 

 hours 



Granite, Ferris j i 

 quarry, core No. 461 1 2 



0.34 

 0.31 



0.77 

 0.84 



2.66 

 2.65 



164. 7\ 

 164.0 J 



0.26 



49-45 



52.8 



.224 



. 210 



Gneissoid granite, i 



Ferris quarry, 



core No. 468 2 



0.32 

 0.25 



0.81 

 0.71 



2.63 i6i.o"j 

 2.6s 162. 8J 



0.28 



67.48 



69.88 



.146 



.145 



Yonkers gneiss, 

 Dinnan quarry 



■ 



2 



0.30 

 0-39 



0.87 

 I .01 



2 .64! 163 .3 1 



1 ) 



2.64 161 .0 J 



0.30 



88.16 



88.16 



.057 



• 057 



Dioritic gneiss, 

 Garden quarry, 

 core No. 459 



I 0.42 0.68 

 2\ 0.24 0.68 



2.83 175-4; 

 2.86 174.8 J 



0.21 62.5 



62.5 



.137 



.137 



Gneissoid granite, 

 Ferris quarry, 

 surface 



I 

 2 



0.37 

 0.98 



0.96 

 2.50 



2 .63 162 .5 ] 



) 



2.62 IS9-4J 



1.08 



86.7 



88.2 



1 



.252 .215 



1 



Granite, Ferris 

 quarry, surface 



I 

 2 



0.44 

 0. 19 



1 . 12 

 0.50 



2.63 

 2.71 



162.3 1 

 167.3 J 



0.40 



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. 



