CHAP. X.] CBETACEOUS PEBIOD. 183 



200 miles. The rapid thinning out of the beds in Dorset 

 shows that they did not reach much farther due east, but 

 it is very likely that the lake was prolonged some distance 

 to the south-east along the axis of the Channel valley, and 

 there can be little doubt that its waters covered a large 

 part of the area which now lies between England and 

 France. It is not assuming much, therefore, if we sup- 

 pose that the Wealden beds spread as far south of our 

 present coast-line as they do to the north of that line. 

 Now from the coast of Dorset they are known to reach 

 inland for thirty miles, and in Hampshire a line joining the 

 Vale of Wardour with the North Downs is forty miles 

 north of the south coast of the Isle of Wight. If, then, we 

 assign the beds an original length of 200 miles and an 

 average breadth of seventy miles, we obtain an area of 

 14,000 square miles for their original superficial extent. 

 The area may have been somewhat larger, because we do 

 not yet know anything of their extreme southern or 

 northern limits, but, on the other hand, there is reason to 

 think that the eastern end of the lake was not so wide as 

 the western. See map, fig. 4. 



The Wealden Beds have often been spoken of as if they 

 were one massive and continuous delta, and as if a calcula- 

 tion of the area over which they were spread out would 

 give us the superficial area of this delta a misconception 

 which has probably arisen from the idea that the beds 

 were formed in the estuary of a great river. If, however, 

 as is most probable, they were formed in a lake, it is 

 obvious that a massive formation might be accumulated 

 in the lake-basin while only small portions of that basin 

 were filled up by the deltas of the inflowing rivers, so as 

 to be raised above the level of the waters, and it is clear 

 that we can form no idea of the size of these deltas from a 

 calculation of the area of the lake-basin itself. Nay, 

 further, would not the size of these deltas be mainly 



