lxxii PKOCEEDINGS OF THE GEOLOGICAL SOCIETY. [May I9OO, 



detail. It is perhaps strange that the value of such a collection of 

 sections, many carried to a great depth and through beds which do 

 not crop out at the surface within considerable distances, was not 

 at once seen. Such, however, seems to have been the case, and in 

 preparing a Geological Survey Memoir descriptive of a tract that 

 contained many of the sites of these wells, published ten years later, 

 1 was content to give a mere abstract of some of these sections, 

 instead of reproducing them in full, an error of judgment that has 

 been corrected in later Memoirs. 



The collection and publication of such matters of detail is pre- 

 eminently the work of the Geological Survey, whose Memoirs, as a 

 rule, are intended to be works of reference rather than light lite- 

 rature ; and during nearly 30 years that Survey has published records 

 of many hundreds, one may say some thousands, of sections of wells 

 and borings, chiefly in the tract with which we are now concerned, but 

 also in other districts. Smaller, but goodly , contributions for various 

 parts of England are to be found in the Reports of the Underground 

 Water Committee of the British Association and in the publications 

 of many societies and by several authors. 



The detailed knowledge thus gained, as to South-eastern England, 

 has been fruitful in general results, of which the following seem to 

 be the more notable : — 



1. In proving the thickness of the Drift at a large number of 

 places, and in showing that this thickness is often greater, some- 

 times far greater, than had been expected, even to the extent of 

 reaching to below sea-level far inland. 



2. In proving that some of our Crag-beds are of much greater 

 thickness underground than we had reason to think, from our know- 

 ledge of them whero their whole thickness is seen at the surface and 

 is small. 



3. In giving us a much bettor idea of the extent of the Eocene 

 Tertiaries underground than we had before, in parts where they are 

 hidden by wide or thick coverings of Drift or of Pliocene. Over 

 large tracts in East Anglia that are represented as Chalk on old 

 geological maps, we now know that the Drift, etc. is next underlain 

 by older Tertiary strata. 



4. In proving the depth to the Chalk in very many places : so 

 much indeed in our immediate neighbourhood here that it would be 

 a fairly easy, though laborious task, to lay down on a map contour- 

 lines of the depth to the Chalk, referred of course to Ordnance-datum, 

 a work that I hope may be undertaken ere long. 



