80 MONTHLY SUMMARY. 



of Trafalgar- sc[uare and tbat of the Society), correspond in one 

 point ^vhicli is of excessively rare occurrence, wliolly beyond pro- 

 vision, and a pure matter of chance ; out of numerous wells bored 

 by Messrs, Easton, Amos, & Sons, for instance, these two are the 

 only instances in which it has occurred. Whilst boring through 

 the chalk, in both cases, the mstrument came upon a fissure 

 and dropped down a space of several feet. To understand the 

 significance of this, it is necessary to remember that the way in 

 vrhich the water in the chalk finds its way to the surface, or into 

 the sea, is through such fissures. An example of its finding its 

 way to the surface from them may be seen in the river Wandle, 

 which takes its rise at Carshalton, near Croydon, pouring out of 

 its source through such fissures a river ready made. An instance 

 of its falling into the sea out of such fissures may be seen at low 

 water near Brighton, where a succession of vertical fissures, from 

 the narrowest chink to 6 inches wide, occurring at varying dis- 

 tances from each other, pours out an immense <]^uantity of fresh 

 water. Such fissures act as the main channels by which the 

 water in the chalk finds its way to the sea. When a w^ell sunk 

 into the chalk does not fall upon one of these, it is dependent 

 . for water on what may percolate through the surrounding chalk 

 into the well ; but if it hits upon a fissure, it draws its supply 

 from a stream itself, and it will, of course, depend upon its size 

 how far it may be exhaustible. The quantity of water percolating 

 through the chalk, however, is so great, that for all ordinary 

 purposes, any well sunk for some depth in it is sufficient. If 

 a very large supply is not wanted, the only drawback on such a 

 well is that it may be lowered by unusual or continuous pumping, 

 so as to require some time to be given to allow it to refill ; and 

 that in course of time the standing point of the water gradually 

 sinks. A well which has dropped upon a fissure, on the other 

 hand, may apparently be pumped for ever without lowering its 

 standing-point. It draws its supplies from a running stream, as 

 it were, and as fast as it is pumped out it flows in. This 

 remark, however, only applies to the standing-point when it 

 has once been found ; for after the well is opened and first tried, 

 there is always a falling from the effects of pumping until the 

 • proper level is reached. In the Trafalgar-square well, which was 

 sunk in 1844, the pumping of 100 gallons a minute for 48 

 hours lowered its surface 4 feet, and it has ever since maintained 

 the same standing-level, varying only with the season. The 



