THE HYDROGEOLOGY OF THE PLYMOUTH DISTRICT. 117 
Compare this with Dr. Geach's account of the we] Is in the 
cavern : 
" It is not certain whether those wells, though they lie below 
the extremity of the limestone, have a mutual communication or 
not ; but it is highly probable, as the bottom of the largest well is 
clay and its sides are shelvy slate, that these are springs ; and it 
is certain that this shelvy vein of slate, nearly the same kind and 
colour with some seen at Mount Edgcumbe on the opposite shore, 
is continued even to the sea, where two openings at low- water have 
been found, through which it is probable the water of the great 
well discharges itself. w * 
No wells of any importance in limestone deliver water above 
sea-level ; if so, some special consideration can generally be found. 
If the outlets are smaller than would pass the late rains, the 
water in the cavern at Stonehouse will now be much above its 
normal level. Again, a small well opposite West Hoe Cottages, 
on the crest of a limestone cliff, owed its water to a bed of bastard 
rock. 
In Stonehouse, little or no water is to be expected above sea- 
level. Attempts have been made to tap the main supply at other 
points. This in limestone is a very uncertain undertaking; for 
it is possible, indeed it has been done, to bore a deep hole, and not 
strike a water-course. Properly looked for, a magnificent supply 
will be found here, as shown by the Millbay springs, and the 
cavern wells. 
Finally, the rising and falling of subsoil-water, and spasmodic 
discharges at various levels, force on us a few words about con- 
tamination. In Plymouth, contamination of subsoil-water is very 
dangerous, more so than in a porous and homogeneous soil. We 
have here the water flowing in prescribed spaces, very frequently 
in ducts. It is fortunate, in one sense, the effects of contamination 
are so prescribed ; but not so that it may completely foul other 
wells, or discharge itself in tenements. Springs frequently appear 
in basements, and cause much damage ; St. Matthew's Church is 
a case in point. A well in the cellar has lately flooded the floor ; 
and were this water previously contaminated, the results might be 
fatal. In limestone, subsoil- water is collected in large quantities 
more or less stagnant, and about the sea-level, as in Stonehouse, 
Fortunately, on its way to the sea it never approaches the surface. 
* See Appendix I. 
