Yol. 55.] ANJS'IYERSAPvT ADDEESS OP THE PEESIDENT. Ixxui 



Thougli, of course, every opportunity of studying the rocks at the 

 surface should be taken, it must not be expected that they will show 

 the same features when found at great depths, beneath a thick mass 

 of overlying beds. Often it is ascertained that beds which are fairly 

 open in sections that can be seen have their fissures, etc., more or 

 less closed up below ground : for instance, at Eichmond, where the 

 Chalk has been worked horizontally under a great depth of Tertiary 

 beds (from a little under to a little over 300 feet), a very great 

 length of gallery has been driven with the result of cutting com- 

 paratively few fissures, and none of those large, so that but little 

 water has been got ; while in the waterworks for Southampton, 

 placed on the Chalk close to its outcrop, so that there was no occa- 

 sion to sink to a great depth, a very much less amount of gallery 

 has yielded a very much larger quantity of water. 



Moreover, the Kent Company, which gives our largest supply 

 solely from wells, has done comparatively little in the way of 

 driving galleries, but has depended largely on simple wells and 

 borings, which are either on bare Chalk or where there is no great 

 thickness of other beds above the Chalk. 



Again, the underground condition of a rock may vary greatly 

 in places near together. The Brighton Waterworks give a good 

 example of this ; for, while at the Lewes lload Station the fissures 

 in the Chalk are many and small, in the Goldstone Bottom Station, 

 not far to the west, the fissures are mostly large, but few. Yet the 

 two stations are at about the same horizon in the Chalk, and there 

 is no apparent reason for this difference between them. A somewhat 

 similar case is that of Croydon, where the old works, in the town, 

 give a much larger supply, without galleries (or at least with 

 merely short connexions between the wells), than that which 

 is got from the new works, but little lower in the Chalk, at 

 Addington, where there is a great length of gallery. 



These are cited as illustrations of the uncertainty of underground 

 work, an uncertainty with which many of my engineering and 

 8ome <3f my geological friends are fairly familiar ; and they should 

 prepare us to be somewhat cautious in predicting, at all events 

 before we know, and I am eften amused with the confidence in 

 foretelling shown by folk who do not altogether know. 



For instance, quite lately, I have seen a pamphlet seriously advo- 

 cating that the whole and sole water-supply of London should be got 

 by means of wells sunk into the Chalk, presumably (so far as one 

 can make out) within the metropolitan area I Of course, the author 



/2 



