330 PEOF. J. PEESIWICH ON THE KAISED 



Beaches would have been out of the reach of the blown sands that 

 overlie the Raised Beaches of Cornwall and Devon, and tlie valleys 

 would have been much deeper. Taking the concurrent testimony of 

 the two facts, I would conclude that the elevation of the land after the 

 formation of the Baised Beaches did not exceed, if it attained, 120 feet. 



It will be seen by reference to the Map (PI. YIII.) that even this 

 extent of elevation would have converted large tracts of the Bristol 

 and English Channels into dry laud and the old sea-coast into a line 

 of inland cliffs. In the face of these cliffs the Caves on the Gower 

 coast, formed by the waves' and surface-waters at the time of the 

 Baised Beaches, now became the resort of the group of mammalia 

 of which the list is given on p. 306, and of which we have no further 

 traces except in the Rubble-drift that overlies both Caves and 

 Beaches. It was at this time also that the old Dunes drifted on the 

 Beaches. Those sands are therefore contemporary with the Caves, 

 and mark another period of lengthened rest. 



Thus far the order of the successive changes is clear, whiJst the 

 succession of life seems to have been contiuuous from early Qua- 

 ternary times. We now come to a stage showing a marked break, 

 caused by the interposition of the Rubble-drift. There are no 

 passage-beds between the stage just described — with its Dunes, 

 Caves, and lower-level valley deposits — and the alluvial and shingle- 

 beds which rest immediately on the Rubble-drift. Whatever may 

 have been the lapse of time represented by the break, there is 

 no evidence beyond that afforded by the Rubble-drift. It is not 

 represented by buj known sedimentary deposits, and the alluvial 

 beds, which in all instances are next in stratigraphical succession, 

 show a complete break in structure and in continuity of life. 

 The change is great and comparatively sudden. I do not mean 

 sudden in the old sense of the word, but that the change was effected 

 in a comparatively short space of time geologically speaking. 



We have only to take the evidence of facts, as they present them- 

 selves in this case, to recognize the remarkable revolution effected by 

 the intrusion of the Rubble-drift or Head which separates the two 

 stages, and which occupies a position discordant with the deposits 

 which both precede and succeed it. Moreover, whereas those marine 

 and river deposits have a general horizontal bedding, and occupy in 

 given areas definite zones, the Rubble-drift lies on the slopes of 

 hills at all angles and at all levels, and only assumes a horizontal 

 position when it reaches the adjacent plain or valley. 



At Polkestone the ' Chalk-and-flint rubble ' descends from the 

 slope of the Chalk escarpment, and must originally have reached the 

 shore. Amongst the Chalk hills of Mid Kent it ascends to heights 

 of 400 and 500 feet and descends to the Thames level. The blocks 

 of Tertiary sandstone and flint-pebbles in the Rubble cliff at Brighton 

 could only have been derived from those outliers of the Tertiary strata 

 which lie in patches on the Downs at heights of from 500 to 600 feet : 

 and Murchison states that "towards the higher portions of the 

 Downs " Mr. Hennah discovered many years ago the bones of 

 ElfjpJias and Cervus in an angular flint-drift in one of the cavities of 



