Geology of the South-east of Devonshire. 439 



sive a scale to be thus accounted for. There is not perhaps a single valley through 

 which a river, or even a brook, at present takes its course, along which alluvia 

 are not found at elevations such as the existing streams in their most swollen 

 states never have attained. The valleys of the Dart and the Teign afford frequent 

 instances. 



Since 1834, when I gave an account of some of the recent changes to be ob- 

 served in South Devon*, facts of this kind have accumulated so rapidly, and are 

 so generally admitted, that at present it seems necessary to give only a general 

 indication of the nature of the evidence and of some of the localities where such 

 phsenomena may be conveniently observed. 



In the valley near Chagford, and beneath the cidtivated fields on each side of the stream, are thick 

 accumulations oi' granitic sand and pebbles, and from their elevation and extent they prove the action 

 of a river far more considerable than the present one. If we take the course of the Teign downwards, 

 and attend to the sections which its banks afford, we see similar deposits of great thickness presenting 

 that peculiar arrangement so characteristic of fluviatile action, and rising high above the reach of pre- 

 sent floods. These deposits can be traced spreading out at the junctions of the valleys which open into 

 that of the Teign. Another instance of the total inadequacy of the power of the present stream to 

 produce the phaenomena to be observed in its vicinity, occurs in the valley of the Lemon (a small 

 tributary to the Teign), and particularly in that portion of it from Bickington to Holbeam Mill. The 

 steep banks of the stream, and several good sections exposed in artificial openings in the fields show, 

 that accumulations of the same character as those above described, occupy the whole broad expanse 

 of level ground, and indicate the former existence of a river of corresponding width. Above Holne 

 Bridge, north-west of Ashburton, the valley of the Dart presents similar phaenomena on a wide scale -f- ; 

 and from this point nearly to Totness there is continuous evidence of a like kind, the neighbourhood of 

 Staverton in particular affording most instructive instances on both sides of the river. The flat mea- 

 dows about Totness are occasionally covered by the waters of the Dart, but these floods strew no 

 coarse materials over their surface, as the fine silt and sand composing the soil sufficiently prove ; so 

 that the thick subjacent accumulation of blocks and gravel must be referred to a former condition of 

 the river. 



§ 4. Ancient lacustrine deposits. — Though the ancient alluvia of the Dart and 

 Teign show that in several places their waters once spread over considerable areas, 

 yet the only expanse which deserves to be distinguished as an ancient lake is that 

 portion of the valley of the Teign which extends from Bovey to Kingsteignton. 



The uppermost part of the series of deposits which occupies this basin,sofaras the level and unintersected 

 nature of the district exhibits, is what the clay-diggers call " the head," and it consists in some places of 

 horizontal layers of sand, as in the upper and middle parts of the valley; coarse beds, which are often thirty 

 feet thick, occur chiefly along the N.E. side, and it is from beneath these, that most of the pipe-clay is 

 now raised. Good sections may be seen on each side of the lower road to Chudleigh. (PI. XLII, fig. 8, 

 B.) The appearances which indicate that this "head" is of fluviatile or lacustrine origin are the sub- 



* See Proceedings Geol. Soc, vol. ii. p. 102. 



t Mr. De la Beche, in his Report on Devon and Cornwall, gives at p. 411 a section taken at this 

 place. 



3 L 2 



