FROM THE CHALK OF HERTFORDSHIRE. 
135 
once have flowed, as is shown by the extent of denudation they 
have undergone. In North America the canons of the Colorado 
region, and the numerous eroded valleys, now dry, or having but a 
small fraction of the water flowing in them that they must at one 
time have had, bear the same testimony to a greatly-decreased rain¬ 
fall in the present day.* We need not, however, go beyond the 
limits of our own country, nor even of our own county, for evidence 
of this. The numerous dry valleys in the Chalk of Hertfordshire 
and elsewhere are silent witnesses of a former time when rivers 
flowed in them at a higher level than they would do now, for a 
vast amount of chalk has been removed by denudation and carried 
into the sea. The plane of saturation must then have been much 
higher than it is now, and the rainfall much greater. The natural 
inferences are that the rainfall is decreasing, and that the plane 
of saturation will from this in addition to other (cosmical) causes 
become lower. In our generation, however, the effect of the 
artificial lowering of this plane only need be feared, and that it 
is to be feared has been ascertained by investigations which have 
been made on the circulation of water in the Chalk and in other 
permeable rocks. 
The systematic collection of information on the circulation of 
underground waters was commenced in this country in the year 
1874, when, at the meeting of the British Association for the 
Advancement of Science held at Belfast, a Committee was appointed 
for the purpose of investigating the circulation of the underground 
waters in the New Bed Sandstone and Permian formations of 
England, and the quantity and character of the water supplied to 
various towns and districts from those formations. In 1877 the 
enquiry was extended to embrace the Jurassic rocks, and in 1881 
to the investigation of the circulation of water in the whole of the 
permeable formations of England. Thus it was not until the York 
meeting of the British Association, in 1881, at which the Committee 
presented its seventh annual report, that the Cretaceous rocks were 
included in the field of investigation, and therefore the underground 
water in the Chalk has received much less attention from the 
Committee than that in the Jurassic, New Bed Sandstone, and 
Permian rocks; in fact, with the exception of one or two well- 
sections which extend into the Chalk, the only information on the 
circulation of water in this rock is contained in the last two reports 
(those presented in 1889 and 1890), and in each instance the in¬ 
formation is derived from papers by Mr. H. George Eordham on 
the height of water in wells in the north of our county, which have 
appeared in our ‘ Transactions.’ f 
Many years before this Committee was appointed, however, the 
subject of underground water in the Chalk had received a con¬ 
siderable amount of attention. The late Bev. J. C. Clutterbuck 
was, I believe, the first who thoroughly investigated it. In 1840 
he wrote a letter to Sir John Sebright, which was published in the 
* For authorities see Prof. Hull’s ‘Text Book of Physiography,’ pp. 176-180. 
t ‘ Trans. Herts Nat. Hist. Soc.,’ Yol. Y, p. 20 ; Yol. Yl, p. 31. 
