Porosity of the Bocks of the Karroo System. 
173 
pore-space lies between maximum and minimum values. Excepting in the 
case of one of the Vereeniging sandstones the maximum porosity reached 
falls far short of the theoretical minimum of 26 % for a rock composed of 
uniform grains packed in the closest manner possible ; the discrepancy 
\ 
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Z-'fO ^'SO . Z-60 . jz-yo 
*S>/>e.c/r/c Q r a y / 
Diapfram showing Dependence of Porosity on Specific Gravity. 
is obviously due to the presence of particles much smaller than the 
average and to finely divided matter partially filling the pores. 
Decrease in density beyond the limits here plotted means that the 
samples have become more open in texture and less coherent by loss of 
* C. S. Slichter. Nineteenth Ann. Eept. United States Geological Survey, part 2, 
p. 310, 1899. 
