CHAP. X.] CBETACEOFS PERIOD. 179 



ground as they do now, and between these districts over 

 the Midland counties of England, and over the space now 

 occupied b j the Irish Sea, and thence by the North Channel 

 round the west of Scotland, spread a fertile lowland dis- 

 trict formed of the newly emerged Jurassic strata. 



In the Wealden area an extensive series of freshwater 

 deposits was in process of formation, a series which is 

 generally spoken of as the delta of a great river, and is 

 usually compared with the deltas of rivers like the Nile 

 and Mississippi, which empty themselves into the sea. It 

 does not seem likely, however, that the area occupied by the 

 Wealden beds was the head of a marine gulf or bay, for it 

 is difficult to see in which direction it could have commu- 

 nicated with the open sea ; the absence of Neocomian de- 

 posits over Belgium and the north of France points to the 

 existence of land on the east, and there is no reason to sup- 

 pose that the Palaeozoic areas of Devon and Cornwall were 

 then separated from those of north-western France by 

 anything deeper than the valley of a river. Moreover, 

 the delta of a large river entering the sea is generally, if 

 not invariably, composed of alternating estuarine and 

 freshwater beds, whereas the Wealden series is entirely of 

 freshwater origin ; hence many have regarded the formation 

 as a purely lacustrine one. 



Such a fluvio-lacustrine origin has especially been advo- 

 cated by Mr. C. J. A. Meyer, who remarks, 1 that although 

 there is considerable variation in the characters of the 

 Wealden deposits, "yet one might venture to say that 

 nine-tenths of the whole was quietly accumulated. The 

 fine-grained sandstones and quartzose grits of the lower 

 beds, the stiff red clays of the middle, and thinly foliated 

 ' marls with Cypris ' of the Upper Wealden might all be of 

 lacustrine origin, and yet include both tree stems and the 

 bones of reptiles. There is indeed in these again, as in 

 1 " Quart. Journ. Geol. Soc.," vol. xxviii., p. 247. 



