Vol. 63.~] OEIGIN OF CEETAIN CANOtf-LIKE VALLEYS. 497 



The Triassic Drift. 



The most noteworthy constituents of these beds are the easily- 

 identified Triassic pebbles from the Bunter, which, although far 

 travelled, occur in great profusion; they also contain flint, and 

 occasionally blocks of vein-quartz, some of the latter being of 

 considerable size. 1 



There can be little doubt as to the course by which the greater 

 part of the Bunter Drift reached the Oxford plain and the valley 

 of the Thames. More than 80 years ago Buckland pointed out that, 

 existing in situ to the north only of the Cotteswold area, drifted 

 Triassic pebbles occur within it 'in prodigious numbers,' as at 

 Shipston-on-Stour, whence he followed them in a continuous trail 

 along the basin of the Evenlode to the Oxford plain, and crossing it, 

 to Goring Gap. 2 The map accompanying his memoir brings them 

 down the Cherwell Valley also ; but, so far as my observations go, 

 they are seldom found there, the gravels of that district being almost 

 entirely Jurassic. 3 The main stream of the Triassic Drift seems 

 to have followed the Evenlode route. 4 



Tracing the Bunter pebbles from their probable source in 

 Staffordshire, we find them ascending the valley of the Tame to 

 the watershed of that river, upon which, at an elevation of rather 

 more than 400 feet, they occur in considerable abundance, 

 descending thence into the plain of the Warwickshire Avon. Not 

 only do they cover a large area in the basin of the latter river, 

 following its course to the south-west towards Evesham, but they 

 again ascend, rising southwards more than 200 feet up the valley 

 of the Stour to the plateau separating it from that of the Evenlode. 



1 The papers dealing with the gravels of this district in recent years have 

 been very numerous. In addition to those already quoted I may mention : — 



H. W. Monckton, Quart. Journ.Geol. Soc. vol. xlviii (1892) p. 29; vol. xlix 



(1893) p. 308 ; & vol. liv (1898) p. 184. 

 H. W. Monckton & E. S. Herries, Proc. Geol. Assoc, vol. xi (1889-91) 



p. 13. 

 A. E. Salter, Proc. Geol. Assoc, vol. xiv (1896) p. 389 ; vol. xv (1898) 



p. 264 ; vol. xix (1901-1906) p. 4 ; & Trans. Herts Nat. Hist. Soc. vol. xii 



(1904-1905) p. 137. 

 H. J. Osborne White, Proc. Geol. Assoc, vol. xv (1897-98) p. 157 ; vol. xvi 



(1899-1900) p. 251 ; vol. xviii (1903-1904) pp. 300 & 414 ; & vol. xix 



(1906) p. 371. 

 Eev. A. Irving. Quart. Jo urn. Geol. Soc. vol. xlvi (1890) p. 557 ; & Proc. 



Geol. Assoc, vol. xv (1898) p. 224. 

 O. A. Shrubsole, Quart. Journ, Geol. Soc. vol. xlvi (1890) p. 582 ; & vol. liv 



(1898) p. 585. 

 J. Allen Brown, Proc. Geol. Assoc, vol. xiv (1895-96) p. 153. 



2 ' Reliquiae Diluvianas ' 1823, pi. xxvii. 



3 I noticed these gravels in two places, at Rousharn on the right, and at 

 Kirtlington on the left, bank of the river. At both Jurassic material greatly 

 preponderates. The gravels contain a few flints or Triassic pebbles, but have 

 little resemblance to the Evenlode gravels in which such detritus occur in 

 great abundance. 



4 Mr. Shrubsole says, moreover, that there is no quartzite-gravel in the 

 higher Windrush valley, Quart. Journ. Geol. Soc. vol. liv (1898) p. 593. 



2n2 



