TRANSACTIONS OF SECTION C. 543 



yellow band forms the upper boundary, defining it from the lower white chalk 

 without flints. 



The lower white chalk without flints No. III. is composed at its base, of a hard 

 nodular chalk, the grit-hed of Price, and it becomes .softer and whiter as far as the 

 flrst layers of flint, which form the arbitrary line of demarcation, between the lower 

 and upper chalk. The latter, comprising Nos. IV., Y., VI., looser in texture and more 

 calcareous than the beds below, needs no special comment in this place. Tlie 

 beds dip steadily to the eastward at a low angle, so that the base of the clitt's 

 to the west of Dover is composed of the lower beds, and to the eastward of the 

 upper. 



The French Cliffs. 



The cliffs between St. Pot and Sangatte reproduce all the characters of those 

 between Folkestone and Dover, the subdivisions being easily ideiitified, and the 

 thickness of No. II. being very nearly unchanged. The beds, too, dip to the east, 

 but at a higher angle. 



The continuity of these rocks beneath the Channel is proved by the researches 

 of the French Channel Tunnel CompanJ^ 



Faults and Dislocations. 



The next question to be con.sidered is, ' Are these strata broken by faults and 

 dislocations ? ' Numerous faults and dislocations are to be seen in the English and 

 French clift's ; but none of them are of great extent. The greatest throw on the 

 English side, which I have observed, amounts to about eighteen feet, and on the 

 French to twenty-flve feet. In the lower part of No. II. the faults are closed fis- 

 sures, not offering free passage to water, a fact proved not merely by the clifl-sec- 

 tions, but by the results of the experimental tunnel driven along the face of 

 Shakespeare's Cliff. There they are niereh' dripping lines of weakness, easily stopped 

 by ordinarj' appliances. On the French side the roclis are more broken, but no 

 difticulty is experienced in drainage. The faults and dislocations in the beds above 

 No. II. which form the cliffs to the east of Dover offer generally free passage to 

 water and are open fissures. In Sir John Ilawkshaw's boring at St. Margaret's 

 Bay, a fissure three feet deep was met with, at a depth of more than 200 feet 

 below the sea-level, and full of salt water. It is clear, therefore, that these rocks 

 are penetrated by open water channels, which underneath the sea draw upon the 

 salt water. This one, be it remembered, was casually hit upon in a small vertical 

 boring. How many, it may well be asked, are likely to be intersected in a tunnel 

 some miles long ? They may be expected to prove a most grave element of danger 

 in the course of working, and to be only made water-tight at a vast expense. Thus 

 there is a difference of the greatest importance between No. II. and the beds above 

 it, the faults and fissures which are closed in the one being open, and water-bearing 

 in the other. 



The Poi'osity of the Beds. 



There is also the same diff"erence to be noted in tlieir porosity, for while the 

 middle and lower parts of No. II. are, for all practical ])urposes, impervious, away 

 from faults and dislocations, the beds above No. II. to the east of Shakespeare's 

 Cliff and to St. Margaret's are highly charged with water, as might be expected from 

 their being continuous with those which supply London with chalk water. Thev 

 form one series of water-bearing rocks. 



The impervious character of No. II. is due to the large percentage of clay 

 mingled with the chalk. Ou analy.sis I find it to be as follows : — 



Per oentnm 

 of clay 

 No. III. Lower wliite chalk at 80 feet above yellow band . 5-7 



» >j » ^"-' <> )> • 2"6 



)» )) !t -''-' » ;> • i8'5 



= Nodular Chalk 



