ON THE CIRCULATION OF UNDERGROUND WATERS. 149 
The daily registration of the heights of the streams might easily be 
made on gauges, painted on the county bridges, but the organisation 
necessary to carry this out is entirely beyond the scope of the British 
Association, and should be carried out at the national charge, being of 
the highest importance to the country. 
The determination of the number of cubic feet of water, carried down 
at selected points on the English rivers, particularising whether it repre- 
sents dry-weather, average, or flood-flow, would be of very high value, and 
might well be undertaken by the Association. Such observations, stating 
the run off per square mile of drainage area and the geological character 
of the area drained, would have more than a local value. 
Permeable rocks below the permanent water-level of a district may be 
regarded as a reservoir of which the cubic content is limited by the size 
of the spaces between the grains, and the width of the fissures and cracks 
by which the rock may be traversed. The quantity of water such rocks are 
capable of storing, has had much light thrown upon it by the investigations 
of Mr. Wethered, published in the fourth appendix to the eighth report. 
The following figures give an abstract of his results as to some of the 
most typical rocks examined by him :— 
Gallons of water absorbed 
bey square inch of rock) 
Rock Locality a he 
Cubic foot of | 3 feet thick 
Old Red Sandstone . . | Bristol 642 53,754,000 
Old Red Flags. F 3 . | Caithness ‘. ‘086 7,254,000 
Old Red Conglomerate . . | Gloucestershire 5 eile 98,000,000 
Carboniferous Limestone . | Clifton F 010 887,000 
” — Oh) eae “049 4,122,000 
Millstone Grit. Bristol . : ; 058 4,853,000 
South Wales (very ° Sse | = 
AL Aerasy 355 28,747,000 
” ae c : Forest of Dean ; CIM ES) 93,625,000 
Pennant Grit . : : . | Bristol . : : = as 
so ir sey ¥ 112 9,446,000 
Sey Grit mt a a } ] 273 22,910,000 
| Bunter Sandstone . . | Heidelberg. : "838 70,889,000 
Magnesian Conglomerate . | Clifton . ah ts 133 11,168,000 
9 Limestone. 2 rf 5 ’ ; 1-044 87,363,000 
Soemmstolie@hard).:° . ..| Bath .. . . 1-473 123,268,000 
Bran '- 198 (soft) . . . ” . . . 2°157 j 180,415,000 
Inferior Oolite (Buildingstone) | Cheltenham .. 1496 — |: 125,147,000 
” » (Pisolitic) 3 : , “146 12,264,000 
Mr. Wethered draws attention to the chemical analysis of the top-bed 
of the filter-beds of the Chelsea Waterworks, which corresponds with the 
analysis of the Millstone Grit and of Pennant Grit. In both cases there 
is nothing in the chemical composition of the filtering medium which can 
oxidise the organic impurities of water passing through. The oxidation 
in the filter is effected by air between the grains of sand, and in the rocks 
by air collected in the interstices; and he points out that with water 
yielded through fissures and joints in the strata, as is the case with the 
