220 MR. A, STRAHAN ON THE ORIGIN OF —_——[ May 1902,. 
the low-lying Oolitic region flow eastward against the general run 
of the country, and make their way through the Chalk-escarpment 
to the Thames or Frome. The explanation did not escape Ramsay. 
Their courses were initiated upon an eastward slope of Chalk, and 
the distance from their sources to the existing escarpment is a 
measure of the recession of the escarpment since the initiation.’ 
The amount of denudation accomplished in this main escarpment: 
is not out of proportion to that which has cut back the North and 
South Downs of the Wealden area to their present position in the 
same period of time. The original position of the escarpment, 
therefore, coincided closely with the water-parting of the eastward- 
flowing rivers. But the general dip of the Chalk is sufficient to 
carry it high into the air over the line of the water-parting, and it 
is evident that it cannot have continued westward. In other 
words, there must have been an anticline along the lne of the 
water-parting. Traces of such an anticline have been detected by 
Mr. Buckman in the Vale of Moreton.’ 
We may now compare this main water-parting of the South 
of England with that of South Wales. From both, the rivers 
take a normal eastward course. On the west side of the one 
the rivers are deflected to a south-westerly course, as in the 
case of the Avon and Severn, or to a north-easterly course, 
as in the case of the Ouse and Nen. Along the other a similar 
deflection takes place, as in the case of the Teifi, or of the various 
streams previously described. ‘The Chalk-escarpment again, in 
Suffolk and Norfolk, where the tilt is less pronounced, ceases to 
form a water-parting, as was the case with the Llandilo, Cribarth, 
and Neath axes in Wales. Lastly, the axis of upheaval in. the 
Chalk is parallel to the Caledonian disturbances which initiated the 
Welsh rivers, and took place in that area in which the geographical 
arrangement of those lines of disturbance would have led us to look 
for it. I infer, therefore, that the initiation of the South- 
Wales and South-of-England river-systems, and the 
southward deflection of the Severn were due to one 
and the same movement, and that in that movement, 
though accompanied by east-and-west folding in the 
Loudon and Hampshire Basins, the Caledonian direc- 
tion was paramount. 
VI. Dave or tHE INITIATION OF THE RIvER-SYSTEMS. 
Evidence for the age of the Caledonian movement, though deficient 
in South Wales, is fairly definitein England. The movement took an 
equal share with the Armorican folds of the London and Hampshire 
Easins in determining the Thames and Frome systems, and was 
presumably contemporaneous with them. But the age of those 
Armorican folds is definitely fixed by two facts. They were post- 
| The existence of certain valleys breaching the escarpment, but not now 
cccupied by streams, is explained by Prof. Gregory, ‘ Natural Science’ vol. v 
(1894) p. 97, on the supposition that they carried the drainage Fr om that part 
of the Chalk-plain which has perished. 
> Quart. Journ. Geol. Soc. vol. lvii (1901) p. 146. 
