Ch. XIX.] 



COOMB NEAE LEWES. 



277 



not have been suspected by the geologist, had not the evidence of great 

 convulsions been clearly exposed in the escarpment of the valley of the 



Fia S26. 



The Coomb, near Lewes. 



Ouse, and the numerous chalk-pits worked at the termination of the 

 Coomb. By the aid of these we discover that the ravine coincides pre- 

 cisely with a line of fault, on one side of which the chalk with flints (a, 

 fig. 327) appears at the summit of the hill, while it is thrown down to 

 the bottom on the other. 



Fig. 327. 



"Coomb l.-".v?-;- : " 



Fault coinciding with the Coomb, in the Cliff-hill near Lewes. Mantell. 

 a. Chalk with flints. b. Lower chalk. 



In order to account for the manner in which the five groups of strata, 

 2, 3, 4, 5, 6, represented in the map, fig. 320, and in the section, fig. 321, 

 may have been brought into their present position, the following hypoth- 

 esis has been suggested : — Suppose the five formations to lie in horizontal 

 stratification at the bottom of the sea ; then let a movement from below 

 press them upwards into the form of a flattened dome, and let the crown 

 of this dome be afterwards cut off, so that the incision should penetrate to 

 the lowest of the five groups. The different beds would then be exposed 

 on the surface, in the manner exhibited in the map, fig. 320.* 



* See illustrations of this theory, by Dr. FittoD, Geol. Sketch of Hastings. 



