530 
Mr. Buckland on the 
chalk, (the indurated varieties of which are well known as the 
puddingstone of Herts, their common state being that of the loose 
gravel beds of Blackheath). These pebbles are composed of chalk 
flints rolled to the same extreme degree as the quartzose pebbles of 
the new red sandstone formation, and having received their attrition 
at a period subsequent to the consolidation of the chalk, and long 
anterior to the last universal deluge. Both these pebble beds, formed 
at periods far distant from each other, have shared the common fate 
of all strata, in being broken up and ravaged by the waters of that 
deluge, and mixed with the angular gravel which was torn by them 
from rocks which had undergone no other previous attrition. And 
accordingly we find rounded pebbles derivative from the plastic clay 
formation mixt with the angular and imperfectly rolled chalk flints 
which constitute the great bulk of the London gravel ; the latter 
having undergone no further attrition than that to which it was 
exposed during the short period of the last great deluge that has 
overwhelmed the earth. 
In the gravel of the valley of Oxford we also mark the same 
distinction between angular and completely rounded pebbles ; the 
fragments of the neighbouring hills being angular, and slightly 
rolled, and those only being completely rounded that can be traced 
up to ancient gravel beds, forming part of the new red sandstone 
strata of Warwickshire, the pebbles of which have been shewn to 
have received their attrition at an early period in the history of the 
revolutions that have affected the surface of our planet. 
A difficulty occurs frequently along the base of a mountain chain, 
in marking the exact line which separates the deposits of post- 
diluvian detritus, which have been and still continue to be drifted 
down by wintry torrents, from that gravel which is strictly of 
diluvian origin. The bursting of an Alpine Lake (such as occurred 
