542 REroRT — 1882. 



is that of coral isles, lava-flows, accumulations of ice, and of sediment in deltas, 

 estuaries, and along sea-coasts. In these cases, unless there are counteracting 

 ao-ents, subsidence invariably follows, and littoral seas are thus areas of depression. 

 The increasing pressure in deep oceanic basins acting on the fluid layer leads to the 

 elevation of lines of least resistance into ridges or dry-land, these lines generally 

 coinciding with coast-lines, and to volcanic outbursts. Geologj' demands pre-eocene 

 communication between many lands. Tlie elevation of land continuous between 

 Europe and America in the north, during the Middle Eocene, was coincident with 

 a cessation in the great formation of basalt, and its subsidence with a renewal of 

 this. The conclusion is drawn that irregularities of surface have and will continue 

 to become more and more accentuated. 



TUJESDA T, A TJQ UST 29. 



The following Papers and Reports were read : — 



1. On the Geology of the Channel Tunnel. By Professor W. Boyd Dawkins, 



M.A.,F.B.S. 



The duty of examining the physical structure of the cliffs on eitlier side the 

 Straits pf Dover, and of collecting all the data necessary for the purposes of a 

 Cliannel Tiiimel, having fallen to my lot, I think it not inopportune to lay the results 

 of mv inquiry before this meeting of the British Association. I will first of all 

 deal with the English dirt's. 



T/ie fiectinn of the JEnr/lish Cliffs. 



The rocks exposed in the cliffs between Folkestone and St. Margaret's consist ot 

 the following in descending order : — 



Thickness 



YI. St. Margaret's Bay chalk 280 + 



V. Nodular chalk with flints 100 



IV. Chalk with few flints 100 



III. Lower white chalk 1.S7 101 



II. Grey chalk and chalk marl No. 2 of Price . . 202 to 2 

 I. ChaEv marl No. 1. of Price = Upper Greensand of old 



authors o to lo 



A. The Gault (Topley) 100 to 120 



Nos. "VI., v., IV. constitute the upper chalk with flints, and III., 11., I. constitute 

 the lower chalk of the English geologists. 



The Gault A, a stiff" blue clay and impervious, forms the low line of cliffs, on 

 the west side of Eastwear Bay, and disappears below low-water mark opposite the 

 Abbot's cliff" tunnel. It has been struck at St. Margaret's Bay in the deep boring at 

 about 5;J6 feet below O. I). 



The lowest bed of the chalk. No. 1., the chalk marl No. 1 of Price, is a clayey 

 calcareous deposit generally impervious, but in some places containing so much 

 ((jlauconite) sand, that it allows of the percolation of water. The sand gradually 

 disappears in the upper layers, as far as the hard rocky chalk, which forms the base 

 of chalk marl No. 2 of Price. From this point up to the top of the grey chalk, 

 there is no great change in the physical character. The calcareous element, how- 

 ever, increases, and the clayey element diminishes. I have therefore in the preced- 

 in<r table grouped the chalk marl No. 2 of Price with the grey chalk, under the head- 

 of No. II., the difference being merely a palaeontological one, the former being 

 characterised by reefs of fossil sponges {Flocosci/phia mceandrina). A well-marked 



