Yol. 54.] AIS-D THE COEALLINE CRAG. 315 



felt also in this country, it may be that in the width of the belt of the 

 Diestien sands between Louvain and Malines we have an approxi- 

 mate measure of the recession of the sea which took place in 

 England between the Lenham and the Coralline Crag periods, and 

 I have ventured so to show it on the map. If this view be correct, 

 it is not difficult to understand that the cliffs which fringed the 

 southern shore of the Coralline Crag sea may have included beds of 

 Lenham or approximate age, from the destruction of which the 

 beach-pebble-like boxstones were derived. They could hardly have 

 come from a Miocene source. There is no indication that the sea 

 of the Bolderien period approached the shores of East Anglia, or 

 that it was connected with the Atlantic towards the south-west.^ 

 It was not until after the close of the Miocene epoch, and in 

 consequence probably of the great disturbances which then ensued, 

 that the German Ocean encroached upon the land over the east of 

 Belgium and the Pas-de-Calais, towards Kent, opening up com- 

 munication with seas to the south-west.^ Moreover, the elevation 

 of the southern part of the Tertiary basin was accompanied by a 

 corresponding depression towards the north, so that the Miocene 

 strata of Belgium were at that period, in all probability, submerged 

 and covered by Diestien beds, and so protected from denudation. 



It is difficult, therefore, from a stratigraphical point of view, to 

 find any other source for the boxstones than the older Pliocene 

 sandstones of the South of England, which, like some part of the 

 sands of Louvain, had, I consider, been elevated into land before 

 the deposition of the Coralline Crag. Originating, probably in the 

 first instance, as beach-pebbles, the boxstones may have travelled 

 as littoral drift along the western margin of the Crag sea,^ 

 or they may have been brought to their present resting-place by 

 the southern currents then prevailing. It should be noticed that 

 they occur almost entirely in one part of the Crag district. That 

 they are found in the same area under both the Coralline and the 

 Bed Crags seems a difficulty, because those two formations must 

 have originated under different conditions. Possibly the nodule-bed 



^ I have indicated in the map (fig. 1. p. 316) the southern and western limits 

 of the Bolderien sea, according to M. E-utot. 



2 It may be noticnd that in the Coralline Crag Miocene shells occur which 

 are found in the Faluns of Touraine, but are not known from the Belgian 

 and North G-erinan Miocene. 



^ The travel of the beach along the south coast of England is now, as it 

 always must have been, from west to east — that is, in the direction of the flowing 

 tide 'The head of the tide,' namely, the point at whii-h the tidal currents 

 running down the eastern coast of England and up the English Channel meet 

 (see Kmahan, Quart Journ. Geol. Soc. vol. xxxiii. 1877, p. 31), is situated at 

 present in t'^e immediate neighb )urljood of the Straits of Dover. If the North 

 Sea during the Coralline Crag period was less open to the north than it is at 

 present, as seems probable (see p. 351), the position of the head of the tide 

 would have been situated farther north than it is now, and the influence of the 

 tidal currents from the south would then have been felt oif the coast of Suffolk. 

 The fac;t that southern currents do not now penetrate to any extent into the 

 Genuan Ocean is probably the reason why so few of the southern species of 

 moUusca found in the English Channel and on the western coast of England 

 occur on the shores of Norfolk, (See Trans. Norfolk & Norwich Nat. Soc. 

 1871-72, p. 42.) 



