THE WEALDEN STRATA 17 



where they are found now. Well, these Paludinas are a 

 kind of freshwater snail ; and, in fact, all the shells we 

 find in the Wealden strata are freshwater shells, till we 

 come near the top, and find the oysters, which live in 

 salt or brackish water. There were quantities in Brading 

 Harbour in old days, before it was reclaimed from the sea. 

 Now, this is a very important point, that our Wealden 

 shells are freshwater shells. For what does it tell us? 

 Why, we see that the first strata we have come to examine 

 were not laid down in the sea at all. Then where were 

 they formed? They seem to be the Delta of a great 

 river, long since passed away, like the Nile, the Amazon, 

 or the Niger at the present day. When these great rivers 

 near the sea, they spread out in many channels, and 

 deposit the mud they have brought down over a wide 

 area shaped like a V, or like the Greek letter A (Delta). 

 Hence we speak of the Delta of the Nile. Some river 

 deltas are of immense size. That of the Niger, for 

 instance, is 170 miles long, and the line where it meets 

 the sea is 300 miles long. Our old Wealden river must 

 have been a great river like the Niger, for the Wealden 

 strata stretch, often covered up for a long way by later 

 rocks, then appearing again, as far as Lulworth on the 

 Dorset coast to the west, into Buckinghamshire on the 

 north, while to the north east they not only cover the 

 Weald, but pass under the Straits of Dover into Belgium, 

 and very similar strata are found in Westphalia and 

 Hanover. The ancient river delta must have been 200 

 miles or more across. 



You must not think this great river flowed in the 

 Island of England as it is to-day. England was being 

 made then. This must have been part of a great con- 

 tinent in those days, for such a great river to flow through, 

 and form a delta of such size. We cannot tell quite what 

 was the course of this river. But to the north of where 

 we are now must have stretched a great continent, with 



