ON THE DIP OF THE UNDERGROUND PALEOZOIC ROCKS. 411 



On the Dbjp of the Underground Palceozoic Rocks at Ware and Clieshunt. 

 By Joseph Francis, M. Inst., G.E. 



[Ordered by the General Committee to be printed in extenso.j 



It has come to my knowledge that some of the geologists specially 

 interested in ascertaining the lie of the ancient rocks beneath the Eastern 

 Counties of England, are doubtful whether any value is to be attached to 

 statements that have been made with regard to the dip of these rocks 

 at certain places. I refer especially to two instances in which borings 

 were made into the strata underlying the Gault to the north of London, 

 and where much time and money were spent in obtaining the true angles 

 and directions of dip. It was in the year 1879 that these observations 

 were made, but it does not appear that any description of the methods 

 adopted has hitherto been published, and Mr. Whitaker has suggested 

 that I should give a short account of the experiments that were carried 

 out by me under the direction of the late Mr. James Muir, the former 

 engineer to the New River Company. This I now propose to do, and 

 hope to be able to show that the recorded results may be accepted as 

 perfectly reliable. 



These borings were undertaken by the New River Company on the advice 

 of geologists who were of opinion that the Lower Green Sand extended to 

 the outskirts of London, and that when found, it could be relied upon to 

 afford a plentiful supply of pure water for the use of the metropolis. The 

 outcrop of the Lower Green Sand to the north of London extends from 

 Leighton Buzzard to Ely, over an area of 166 square miles, and con- 

 sequently must receive on its surface an immense quantity of rain water ; 

 moreover, being extremely pervious, it must be capable of transmitting 

 through its mass a large percentage of the rainfall. Nearly forty years 

 before this, a good yield had been obtained from the same formation, at a 

 depth of 1,800 feet, at Grenelle, near Paris, and later on at Passy, 

 in the same neighbourhood. A deep bore at Kentish Town, made in 

 the year 1855, had revealed the fact that a ridge, if nothing more, of 

 ancient rocks protruded upwards to the Gault, and this discovery raised 

 considerable doubt as to the extent of the sandy layer under ground. 

 There was also a great amount of uncertainty as to whether this stratum, 

 which is so prolific of water when tapped anywhere near its outcrop, 

 would yield equally well where compressed by the Aveight of a thousand 

 feet or more of superincumbent earth. On the other hand, the Royal 

 Commission on Water Supply, which sat in 1869, had reported that 'so 

 far as this Green Sand continued, it would form a valuable and copious 

 water-bearing bed,' and it was felt that the problem was one of such 

 extreme importance that it was of the utmost consequence it should 

 be solved. The water supply, which there was a chance of so gaining, was 

 so convenient and good as to justify some amount of speculation in 

 endeavouring to obtain it, whilst there was, in any case, a certainty of a 

 large accession of Chalk water from the upper part of the bore. I may 

 here remark that, although several eminent men decidedly encouraged the 

 venture, they can hardly be held responsible for the extravagant notions 

 entertained by some persons, who assumed that this experiment was about 

 to solve the whole question of the future supply of water to London. 



