THE MIDDLE LIAS OF NORTHAMPTONSHIRE. 
289 
The results obtained are tabulated below :— 
Table showing data from which the capacity of Marlstone 
Rock for Water was deduced. 
No. 
Specific 
gravity. 
Weight of 
Dry Stone 
in 
grammes. 
Weight of 
Stone 
saturated 
with water 
in grammes. 
Weight of 
Water in 
grammes. 
Bulk of 
Water com¬ 
pared to 
bulk of 
Stone. 
Gallons of 
Water 
per cubic 
foot of 
Stone. 
1 
2-945 
7-870 
8-290 
•420 
•157 
•98 
2 
2-7 
15-16 
16-34 
1-18 
•21 
1-3 
3 
3-0 
46-467 
48-910 
2-443 
•16 
1-0 
4 
2-78 
56*285 
59-236 
2-951 
•146 
•91 
It will appear from this table that the average capacity of 
these particular specimens of rock for water is a little over 
one gallon per cubic foot, and the balance of possible errors 
w r as certainly in a direction tending to reduce the calculated 
capacity. Making an allowance of one-third of a gallon for 
water which would always be retained by the rock under the 
particular conditions in which it is met with in the ground, 
there would still be room for two-thirds of a gallon per cubic 
foot, of what we might call replaceable water. 
One cubic foot = 6’25 gallons, therefore, if one cubic foot 
of rock in its normal condition is capable of receiving two- 
thirds or -6 gallons of water, it is equal to *6 -f- 6*25 = *107 
gallons, or a little over one-tenth of its bulk. Thus, 
neglecting the capacity of the fissures, one square mile of 
rock, 6ft. in thickness, could receive or yield over 111,000,000 
gallons of water. 
What is the Area to be Filled ? — In considering the 
storage capacity of the bed itself, naturally, a volume of 
water equal to nine-tenths of the volume of the fissures 
ought to be added to the estimate given above, for in these 
fissures there is, or might be, a full cubic foot of water where 
only one-tenth has been allowed for. I cannot give the least 
idea what that volume should be, but I may say, without any 
hesitation, that the storage power of the bed as a whole is 
considerably greater than that given for the material of 
the bed. 
On the other hand, six feet, about the average thickness 
of the Rock-bed for the county, is not the average for the 
