250 NEOZOIC TIME. [CHAP. XII- 



western seas, and may never have been wholly submerged: 

 at any subsequent time. The limitation of the Lenham 

 and Diestian Sands to the northern side of this tract, and 

 their apparent absence over the South Downs, are facts- 

 which suggest that their original boundary line, and there- 

 fore the shore of the early Pliocene sea, lay somewhere over 

 the central axis of the Wealden district between the lines of 

 the North and South Downs, as shown in the map, fig. 7 r 

 where the line A A shows the supposed position of this 

 shore-line. 



On the other side of the isthmus above mentioned lay 

 another sea, arms of which probably advanced into what i& 

 now the area of the English Channel. If Mr. C. Reid is 

 right in thinking that the St. Erth Beds belong to the 

 Older Pliocene epoch, a large part of Cornwall may then 

 have been covered by this southern sea, for, as Mr. Reid 

 observes, 1 " the St. Erth clay was evidently laid down in 

 still water, which would not be found at a less depth than 

 40 or 50 fathoms in a district exposed like this to the 

 Atlantic swells. The fossils also in that clay point to 

 some considerable depth of water, while the general 

 flattened contour of the country suggests that this district 

 has nearly all been submerged within a comparatively 

 recent period. The lower parts of Cornwall form a smooth 

 undulating country, out of which rise abruptly the higher 

 hills. Round one of these hills, St. Agnes' Beacon, coarse 

 sand is found at a high level. This is probably a beach 

 deposit of the same age as the clay at St. Erth, though all 

 fossils have now disappeared from it. Cornwall seems at 

 that period to have formed a scattered archipelago like the 

 Scilly Isles." 



It must be admitted, however, that the separation of 

 these two seas is a doubtful question, and the mere absence 



1 "Nature," Aug. 12, 1886, p. 342. 



