1866.] TYLOE — VALLET-GRAYELS. 465 



many MoUusca now living in tranquil water in tlie neighbourhood 

 and on the same horizon, and also of three species of Mollusca which 

 have disappeared from the country, one species not being met with 

 now at any nearer point than the Mle. To suppose that man was 

 living throughout the period of the lower valley-gravels at the same 

 time as the great extinct Mammalia, obliges us to carry back his 

 presence on the earth not only to a very distant date, but to a period 

 when physical circumstances must have differed very much from those 

 we experience. We therefore wonder that there are so few indica- 

 tions of his presence or works left behind ; for we cannot realize the 

 lapse of time without fixing on some events by which to measure it. 

 If man existed prior to so great and distant an event as that of the 

 excavation of the valleys, the problem becomes still more difiicult to 

 understand. 



The opinion of Mr. Prestwich as to the age of the Somme valley 

 is not at present confirmed, as far as I am aware, by any other geolo- 

 gist. Sir H. T. De la Beche thought the valleys of Devon and Corn- 

 wall opening into the English Channel might have been excavated 

 not later than in early post-Cretaceous times, but that their forms may 

 have been modified more recently. Mr. Godwin- Austen thinks the 

 German Ocean and English Channel were not united at the period 

 of the Coralline and Eed Crag, so that the easterly part of the 

 Channel would have been formed in the Pleistocene period — a view 

 now generally adopted. 



Also Mr. Pengelly considers that the valleys of the south-east of 

 Devonshire were excavated in post-Cretaceous times, and were sub- 

 sequently filled from base to hiU-top — a point also discussed by Sir 

 H. T. De la Beche mthout his arriving at a definite conclusion*. 



Mr. Pengelly distinctly refers the reopening of the valleys to a 

 subsequent denudation, and remarks, " A remnant of the gravel re- 

 mains to line the slope and preserve a record of the operations " f. 

 He does not give any sections ; but, having visited some of the local- 

 ities, I concur entirely in his opinions. Mr. Pengelly asserts that he 

 has also discovered perforations made by a marine boring-animal at 

 considerable elevations above the sea and above raised sea-beaches, 

 in many localities in the Torbay district ; and I give the following 

 sections of valleys, that the position of these bored holes may be 

 clearly understood. 



In the valley leading to Kent's Hole Cavern (fig. 1) there is red drift 

 on the plateau, and the same material in the cavern and on the bottom 

 of the valley ; this is usually the case in the district. If the borings 

 in the limestone forming the face of the cliff in which the openings 

 into Kent's Hole Cavern occur, at a height of 180 feet above the sea, 

 have been made by a marine animal (Pholas, or any other borer) 

 then it is good evidence that the drift has been removed from the 

 narrow and short valley below the cave, leaving no marks of denu- 

 dation on the valley itself. "We have therefore no evidence in Kent's 



■"^ I may add that the fringes of gravel along the Devonshire valleys were 

 noticed by Mr. Grodwin-Austen in an early paper. 

 t ' Denudation of Rocks in Devonshire,' 1864, p. 19. 



