242 PROCEEDINGS OF THE GEOLOGICAL. SOCIETY. 



Not having sufficient data to give the dip of the Chalk throughout these 

 sections, I have preferred leaving out the stratification altogether, and 

 merely inserting the Clialk as a rock-mass under the Tertiaries (see below). 



These lines of sections do not fellow a straight line, — the variations of 

 directions are indicated approximately. The horizontal scale is about 7 

 miles to the inch, and the vertical scale 20i)0 feet to the inch. 



The numbers under the names of places denote the height of the spot in 

 feet above the sea-level. 



The black shading marks the depth of water in the Channel and the 

 Thames. 



The zones 6 and 7 are left blank, as their correlation is not treated of 

 in this })aper. 



For the divisions of the Sables inferieurs of M. d'Archiac see p. 208 ; 

 also Table. 



All the Faults and minor disturbances are omitted in both sections. 



Diagram. As the scale of the preceding sections does not admit of any 

 detail in the structure of the lowest group of the Tertiaries — that between 

 the Chalk and the Loudon Clay — I have here given a theoretical restora- 

 tion ol" these beds as presumed to have extended from London to Paris. It 

 is, in fact, a magnified representation of zone No. 1 of both the Sections 

 above, irres])ective of the present configiuation of the siuface. 



The vertical dotted lines denote the position of the })roved and complete 

 local sections on which the whole series is established, whilst the chief 

 places at which each member of the series can best be studied is indicated 

 by the names attached to the corrcs})ondiug letters. 



The distances are only approximately preserved in this diagram. The 

 scale of depth is one inch to 200 feet. 



The stratification of the Chalk is not given, for the same reason as men- 

 tioned with respect to the sections. I may state, however, that beneath 

 the Tertiaries at Paris, the Chalk has been found to be 1-100 feet thick ; 

 whilst at Lille the Tertiaries repose upou Chalk-strata only 217 feet thick 

 and overlying the Caiboniferous Limestone ; at Calais, the Chalk beneath 

 the Tertiaries again atiaius a thickness of 7(^^ feet, reposing upon the 

 Coal -uu»asures ; and at London of ()45 feet, resting on the Upper Green- 

 sand and Gault. 



For the evuleuce on ^^hicll that ])ortion of the Diagram which extends 

 from Chobham to Kichborough is founded, see my paper "On the Woolwich 

 and Keadiug Series," in Quart. Joiu-n. Geol. Soc. vol.x p. 7'^-170, and Plate. 



At Calais, the well-section showed, under 85 feet of recent deposits and 

 20 feet of London clay, beds which I should group thus : — 



foc-t. 



Greenish sands with traces of shells 10 \ Baseme7it bed of the London 



Large tlint-iH-bblcs 3.^ J Clay? 



Ligl\t-eolourc(l green sands ; traces of shells... 32 Woolwich and Reading series. 



Very tine light-groy sands 17 



Clayey sands with traces of shells S 



Compact sandy clay 11 



Hard brown clay with traces of shells 23 



Hods of clayey grey and greenish sands 19 



Bcdof tlints in clay ^ 



Chalk. 



As the specimens were much crushed by the auger, 1 could not determine 

 any of the shells. Between Calais and Cassel I have no sections, except 

 shallow surface-sections at Watten, where I recognised the London Clay. 



Thanet Sands. 



