iReprinted from the Report of the British Association, 1882.] 
llorositu aiib lleirsitg of |iocks foitlj itgark 
fa Mater §np|!ii. 
By E. WETHERED, F.G.S., E.C.S. 
Y first object in commencing a series of observations on the 
Jj/A, porosity of rocks was with a view of investigating the 
lithological changes which are brought about by the percolation 
of water through them. But while engaged in work of this 
kind, one is struck with the great volume of water which the 
rocks of the earth are capable of absorbing, and a knowledge of 
this is important both as regards water-supply and the suitability 
of stone for building purposes. Much information on the subject 
has already been obtained by the investigations of the Rivers 
Pollution Commission, the Commission on Water Supply, and 
on the Selection and Deca}?’ of Stone for the Houses of Parlia- 
ment. Also by the Committee appointed by the British 
Association for the Investigation of the Circulation of Under- 
ground Waters, and bj^ Mr. De Ranee, C.E., F.G.S., in his 
book on the Water Supply of England and Wales. 
The method which I have adopted for arriving at the results 
contained in this paper is that recommended by Dr. Sterry tl unt 
in the Geological and Chemical Essays.^ The portions of rock 
selected for the work were struck off by a blow with a hammer. 
By this means I was enabled to get clear and natural surfaces 
Pages 165-7. 
