430 THE CRETACEOUS SYSTEM. CHAP. 



of my own procuring. From other sources e I collect similar re- 

 sults, though with some diversity, according to opportunities 

 and varying personal views, especially as to the proportion 

 of the fossils which may be regarded as truly of the age of the 

 deposit. 



Under what natural conditions could specimens from these 

 various sources meet in this solitary and limited drift? In the 

 Wealden we see the effects of downflowing land-streams ; and, 

 according to ordinary interpretation, the currents at last filled 

 a large estuary. The river flowed and the rain-torrents swept 

 over wasted surfaces of strata older than the Wealden, which 

 yielded plenty of iron-oxide. But the typical Wealden beds con- 

 tain no drifted fossils from older strata. The Potton sands must 

 have had a similar origin the waste of older land rich in oxide 

 of iron they may have been derived from the same land, but they 

 require in addition a local action of a different kind, competent to 

 yield quite different results. This action I believe to have been 

 the beating of the sea on wasting cliffs of the Oxonian and Port- 

 landian, perhaps also the older Wealden rocks. 



To carry out this general view a very large extent of waste 

 must be supposed to have happened on a range of coast where now 

 extend the undulated surfaces north of the iron-sand ranges, for 

 it seems reasonable to suppose the region to the south was deeper 

 water for some not very considerable breadth on the northern slope 

 of the ancient anticlinal of Harwich. It is possible indeed that 

 such depth may not have there prevailed, and that from that side, 

 on the contrary, came the ferruginous sediments, just as it may 

 have happened that the similar Wealden sands and ' lower green- 

 sand' were derived from the southern slopes of the same anticlinal. 

 It is not easy to obtain them by stream-action from the far north, 

 and there is no sufficient reason yet established for admitting them 

 to have come from the far west, the direction in which one is 

 sometimes tempted to look for the local origin of all this thick 

 mass of littoral, estuarine, and fluviatile sands. 



While the Faringdon beds are full of the remains of resident 

 life, or of marine creatures contemporaneous and vicinal, if not living 

 on the spot where we find them, and the Shotover beds contain 



e The literature of the Potton deposit is already extensive, including notices by 

 Brodie, Walker, and Seeley in the Annals and Magazine of Natural"History. 



