107 



IV. — Coast Erosion. 



The coast line from St. Margaret's Bay to Folkestone has 

 been compared with the six inch ordnance map of 1876, since 

 which date there has not been any noticeable loss of land, but 

 only the heavy falls previously mentioned. 



At 24 principal, and 11 intermediate stations, holes have been 

 drilled in the chalk on the plane of marine erosion ; these are half 

 inch holes, three inches deep, having a different arrangement for 

 each year thus : — 



1890. 1891. 1892. 1893. 



o . o . o . 



The hole with the circle round it is the test hole, the others 

 are only indicating marks. 



This form of mark was chosen as not being easily imitated 

 or tampered with. The average erosion of four years has not 

 been more than half an inch, and this is somewhat surprising as 

 the chalk, with the exception of the hard nodular beds, cannot be 

 considered a hard rock, but it possesses a toughness that renders 

 the boring of these half inch holes with a brace of five inches 

 radius, a considerable exertion. The great falls seem to be caused 

 by the springs sapping the foundations, the sea afterward carrying 

 away the fallen blocks. 



Some years ago a careful investigation was made of these 

 springs in connection with schemes of water supply when two 

 hundred of considerable volume were stated to issue out of the 

 base of the cliffs between Folkestone and the South Foreland. 



S. GORDON McDAKIN. 



XXVII. 

 CHEMISTRY OF DOVER WATER. 



BY 



W. H. PENDLEBURY, Esq., M.A. (Oxen.) F.C.S. 



In these days of general enlightenment it is hardly necessary 

 to insist upon the importance of a pure water supply, since almost 

 everyone is aware that the health and well-being of every community 

 depends, in great measure, upon its having pure air and pure water. 

 The object of my paper is to indicate what impurities are present 

 in the Dover water supply, and to show experimentally how 

 the impurities may be detected, and, if necessary, removed. I must 

 ask you to disabuse your minds of the idea that the word 

 "impurity" necessarily implies the presence of a harmful sub- 

 stance. Absolutely pure water is a compound of the two gases 



