208 
BORING AT SHILLINGFORD. 
Sep., 1891. 
waters rise from below along lines of fault or fissure ; while 
in the Shillingford case the difficulty is further increased by 
the fact that the water supply from the lower horizon, instead 
of being salter than that in the higher beds (as at Swindon), 
is reported to be fresh and drinkable. 
It is indeed unlikely that all the deep-seated saline waters 
in these counties have derived their salinity from the same 
source, and each case must be considered separately. I can¬ 
not but think, however, that, in many cases, the saline 
solutions are not now being introduced from any extraneous 
source, but are either derived directly from the materials of 
the rocks in which they occur or from salts left by the former 
passage of sea-water through these rocks, and preserved 
in certain localities under special stratigraphical conditions. 
I am disposed to think that in the case of the Shillingford and 
Didcot borings the salinity of the water found in the Vectian 
sands may be due to the peculiar stratigraphical position of 
these sands. They rest unconformably on the Kimeridge 
Clay, and they are often overlapped by the Gault. The 
general dip of all these strata is to the east-south-east, and 
their out-crops sink to lower and lower levels as they are 
followed across the country toward the valley of the Thames, 
both from west to east in Berkshire, and from north-west to 
south-east in Oxfordshire. In consequence of this inclination 
the natural direction of flow for water percolating through the 
sands beneath the Gault would be eastward toward the 
London basin. 
Judging however, from the irregular and discontinuous 
occurrence of these sands along their line of outcrop in Oxford¬ 
shire and Berkshire, it seems probable that their easterly 
continuation may be equally discontinuous, so that it is quite 
possible that at a distance of a few miles east of Shillingford 
they may be overlapped and completely cut out by the Gault ; 
this clay coming into apposition with the Kimeridge Clay for 
a certain space as it does near Culham. If this were so, and 
even if the Vectian sands were perfectly continuous to the 
southward or northward, but rising to higher levels, the water 
in the sands below the Thames Valley would be backed up, 
and though there might be egress to the southward at some 
higher level, yet there could be no rapid outflow. The water 
in the lower part of the basin would be, to all intents and 
purposes, stagnant, and the outward diffusion being slow, it 
would become saturated with salts and mineral matters 
dissolved from the ferruginous sands in which it lay. 
