Rev. A. Irving — Water Bupi^ly from the Bagshot Beds, etc. 23 



the well-section at Wallingford, as it is ia the Culham section, by a 

 few inches only of dirty green sand. It is possible that the well in 

 question has tapped an underground reservoir consisting of an 

 aiicient lagoon-deposit or silted-up lake ; and if this be the case, 

 the pollution of the water with vegetable-matter is accounted for. 

 The absence of the whole of the Portland and Purbeck series, and 

 the extreme attenuation of the Lower Greensand, gives countenance 

 to such a hypothesis. 



2. Going further north, to the little town of Brackley in North- 

 amptonshire, we meet with phenomena somewhat similar to those 

 just described. Here too there is a considerable break in the 

 geological series, as the Great Oolite rests generally in the district 

 upon the ferruginous sands which cap the Upper Lias Clays. That 

 the rich deposit of ironstone, known as the Northampton Sands, owes 

 in part its existence to the agency of vegetable acids, I have little 

 doubt ; ^ but the fact which bears immediately upon our present sub- 

 ject is the occurrence, in the section of the well at the Brackley 

 Waterworks, of twelve feet of " running sand," taking the place of 

 the more highly ferruginous deposits which are commonly met with 

 at this horizon. Nearly one-half (the lower half) of this running 

 sand is of the same character as the dirty green and grey sands of 

 the Bagshot series. A copious supply of water was obtained here, 

 but it was found to be so objectionable as to quality, that it was 

 rejected for the use of the town, and the well was continued down 

 another 100 feet, until it penetrated the more calcareous rocks of 

 the Middle Lias. The water obtained from the sand at a depth of 

 63 to 75 feet (the whole depth of the well being now 175 feet) was 

 described to me as being ' brackish ' ; and there seems little room 

 for doubt that a careful examination of it would have shown it to be 

 polluted with vegetable - matter in solution. Even the water 

 pumped up from the Middle Lias is not quite free from this, and 

 being at the same time slightly charged with bi-carbonate of lime, 

 it deposits a curious amorphous precipitate resembling kaolin in 

 appearance, inside the engine-boiler. This deposit is found to 

 contain some carbonate of lime, but is mainly composed of silicate 

 of alumina, the latter being in all probability precipitated by the 

 decomposition, during the process of digestion which goes on within 

 the boiler, of double soluble salts, formed by the combination of 

 silica and the ' humus-acids ' with alumina as a base.^ 



Looking at the facts of the two cases now cited, we find a certain 

 resemblance between them. In both cases there is a break in the 

 normal geological succession of the strata, and this of course implies 

 more or less of erosion of the lower series at both places. Under 

 such conditions it is extremely likely that in hollows formed by 

 suoli erosion there should have been accumulations of such coarse 

 sandy materials as are characteristic of shallow waters, and that along 



^ Comp. my paper, On the Coloration of some Sands, etc., in the Report of the 

 British Association, 1883. 



2 I am indebted to the courtesy of Sir George Bannerraan, Bart., in bringing the 

 facts conaected with the Brackley well under my notice. 



