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While examining the Plio- 

 cene deposits of Cornwall 

 in 1886, I was puzzled to 

 account for the valley 

 (fig. 1) which crosses Corn- 

 wall from north to south, 

 from St. Ives Bay to 

 Mount's Bay, almost iso- 

 lating the Land's-End dis- 

 trict. This depression is 

 partly occupied by Pliocene 

 strata ; but it obviously did 

 not originate in Pliocene 

 times ; it is something older, 

 something that does not 

 fit in with the late-Tertiary 

 denudation of Cornwall. 

 A more extended know- 

 ledge of Cornish geology 

 suggests that this Pliocene 

 strait was once an Eocene 

 river-valley, now so trun- 

 cated at both ends that we 

 cannot say whether it ran 

 from south to north or 

 from north to south. 



The diagrammatic section 

 (fig. 2) shows the relation 

 of the Land's-End mass to 

 the rest of Cornwall. It 

 will be noticed that at 

 about 400 feet above the 

 sea there is a strongly- 

 marked shelf, or plane of 

 marine denudation, of Plio- 

 cene date, this plane bear- 

 ing no fixed relation to the 

 limits of the granite. The 

 upper boundary of this 

 plane is a degraded cliff, 

 which may cut obliquely 

 across any geological boun- 

 dary. The Pliocene shelf is 

 a striking feature through- 

 out West Cornwall, espe- 

 cially on the windward side. 

 But the Pliocene deposits 

 are not confined to this 

 shelf, patches being found 

 near St. Erth at a much 

 lower level, near the bottom 

 of the wide open valley, 

 which existed before the 

 notch was eroded in its 



