BEACHES, ETC., OF THE SOUTH OF ENGLAND. 331 



the Chalk.^ The Rubble-drift at Chesilton on the northern end of 

 Portland rises from the shore to the height of 200 feet. In Devon 

 this drift occurs on the high slopes of Exmoor and Dartmoor, and 

 in Cornwall it descends from the summit of Beacon Hill (600 feet) 

 to its lower slopes. The great mass of rubble, that extends over the 

 Chalk plain above Didcot to a height of 400 feet or more, comes 

 from strata which southward rise 100 to 200 feet higher. In Gower 

 the Head at Rhos Sili is derived from hills behind, rising abruptly 

 several hundred feet above the Beach terrace ; while the highest 

 well-marked instances of this drift are those (the so-called Old 

 Beaches) on the Cotteswold Hills which attain a height of from 800 

 to 900 feet. 



It is evident that the force — whatever it was — ^which determined 

 the formation of the Rubble-drift acted from above downwards. 

 This, under certain circumstances, might have been the result of the 

 descent from the hill tops of ice and snow, or of water. Ice might 

 have acted in some respects in accordance with the observed phe 

 nomena, but in other respects there are the objections I have already 

 named ; and with regard to rain and surface-waters, the results are, 

 as I have shown, irreconcilable with their agency. But there is 

 another form under which we may consider the action of water, and 

 this, although not free from objections, answers to all the physical 

 conditions of the case. 



It is that of water in a body, not moving rapidly over the surface 

 as in a wave of translation, but displaced from a state of rest, while 

 the land is in process of elevation from beneath it. There is the 

 objection, amongst others, to a wave of translation that it would 

 carry the debris in one prevailing direction, and in each locality we 

 should have foreign elements more or less largely introduced, and 

 the drift assuming a ' crag-and-tail ' arrangement behind the hills ; 

 whereas no such distribution prevails, but on the contrary we 

 have in the area we have described a number of local centres from 

 which the drift diverges in different or in quaquaversal directions 

 and combines in the intervening valleys. This is a result which 

 would necessarily follow on the emergence of land from beneath a 

 body of water, and such seems to me the most probable solution 

 of the problem we have before us. 



I am therefore led to suppose that a submergence of the land 

 which, judging from the heights at which the Rubble-drift is found, 

 could not have been less than 1000 feet, followed immediately upon 

 the epoch of the low-level valley drifts and the Caves. There is 

 little or nothing to show as a direct consequence of the submergence. 

 The land over which the waters spread seems to have undergone 

 but trifling alteration or denudation. The Raised Beaches exhibit in 

 consequence thereof no apparent erosion, and the Blown Sands only 

 slight denudation ; and this may be due to the impact of the Head. 

 It is even difficult to say whether their irregular thickness and 

 eroded surface resulted during the submergence or emergence of 

 the land. I can only conclude that the submergence was slow and 

 1 Quart. Journ. Geol. Soc. vol. vii. (1851) p. 367. 



