ON THE GEOLOGY OE HERTFORDSHIRE. 
89 
As an example of the opposite extreme, a paper by Mr. J. L. 
Lobley (No. 228) may be referred to. He holds the view that our 
rivers derive their supply of water from a very small area in their 
immediate vicinity, so that however vast a quantity of water is 
abstracted from the Chalk throughout the area over which they 
flow, their volume cannot be sensibly affected. As we have large 
tracts of country without rivers, he thinks that the Chalk may be 
entirely deprived of the available water which it contains under 
such tracts without appreciably affecting the rivers on either side 
of them, overlooking or ignoring the fact that it is owing to the 
depletion of our Chalk reservoir from natural causes, now augmented 
by artificial ones, that such tracts, over many of which rivers 
formerly flowed in valleys now dry, are waterless. 
In discussing the future water-supply of London, the late Sir 
Edward Erankland (No. 267) expressed a view which differs from 
either of the above. He evidently thought that the level of the 
water in the Chalk in the catchment-basin of the Thames nowhere 
rises to the surface, for he said : “ The rivulets and streams of 
the Thames basin are formed and pursue their course on clay land. 
There are no streams on the Chalk.” We have not yet arrived at 
this dessicated condition, several of our rivers being augmented 
either in their beds or on their margins by springs which rise 
directly from the Chalk. A little further depression of the water- 
level in the Chalk than would cause them to cease to flow would 
convert their channels into swallow-holes, as is now the case under 
usual conditions in the upper valley of the Colne. 
In the first paper a correct theory is merely carried too far; in 
the second, conclusions are arrived at which are unwarranted by 
either theory or facts. The statement in the third paper may 
become true if our Chalk reservoir is much further depleted. 
One work in the list merits special mention on account of its 
great value. Mr. Whitaker’s ‘ Geology of London and of Part of 
the Thames Yalley ’ (No. 195), a Memoir of the Geological Survey 
published in 1889, is indispensable to students of Hertfordshire 
geology, as may be gathered from the references which I have 
given under its heading. 
I must also mention a very valuable piece of experimental work 
carried out in our county in 1879, but of which the methods and 
results were not published until 1895. I refer to the elaborate 
and carefully-conducted experiments made by Mr. Joseph Francis 
to determine the direction and angle of dip of the Palamzoic rocks 
in the borings of the New Fiver Company at Turnford and Ware. 
The experiments were made under the direction of a Committee 
consisting of Sir William Thomson (now Lord Kelvin), Hr. C. W. 
Siemens, Professor (now Sir George) Stokes, Professor T. McKenny 
Hughes, Professor J. C. Maxwell, Mr. Fobert Etheridge, Mr. F. W. 
Mylne, and Mr. James Muir.* The results were that the Wenlock 
* Mr. Whitaker, to whom I am indebted for a few entries in this List, desires 
me to state that in his Anniversary Address to the Society in 1899 (No. 300) he 
inadvertently omitted to notice these experiments. 
