XXX PfiOCEEDINGS OF THE 



elsewhere — we should find that a very considerable portion of the pebbles were 

 not flints derived from the chalk, but pebbles of older rocks which came with 

 ice-borne deposits from the Midland Counties or even further. This showed that 

 we had at one time a geater extent of g-lacial deposits than can now be traced. 

 Before the glacial period closed, it would appear probable that we had aU over 

 the Chalk and some portion of the London Clay a regular ice-cap, which ground 

 up the chalk and clay into the chalky boulder-clay we now hnd, and earned 

 otf the flints, dragging them one against another, producing the scratched flints 

 so characteristic of the boulder-clay deposits. 



It was not improbable that some of the outlines of the valleys were carved out 

 and subsequently enlarged by the action of rivers and other subaerial forces. 

 The author of the paper spoke of valleys being cut through the boulder-clay, and 

 inasmuch as we had no evidence of submergence, it appeared very probable that 

 denudation had taken place by the action of rain and rivers operating through a 

 long period of time and removing the surface of the ground. 



The question as to whether in former times we had a larger amount of rainfall 

 was one of considerable interest, and it did appear probable that at some geological 

 period there might be a larger rainfall than there was now ; but in all river- 

 valleys there had been another force at work which we did not thoroughly ap- 

 preciate at the present time — rivers were more subject to floods, for the reason 

 that in former times they were not "domesticated." Now we looked after the 

 banks of rivers and removed obstructions, but in former times fallen trees and 

 accumulations of ice stopped up rivers and produced floods, the operation of which 

 would be greater in a few days than in many years if the river had a free and 

 unimpeded course. That was a well-known fact pointed out by Sir Charles 

 Lyell and others long ago, but it was well to bear it in mind. 



There was a great difficulty, as was pointed out, in distinguishing the river- 

 gravels from the older deposits from which the constituent parts have been 

 derived, as in the case of a river rimning through a country where there are 

 deposits of marine gravels, the drift consists of the same ingredients, but 

 arranged in a different manner, and contains land animals instead of marine shells. 

 That made him doubt whether some of the brick-earths which contained remains 

 of the reindeer and mammoth did not belong to the Post-glacial instead of the 

 Pre-glacial period ; but it was shown that the mammoth did exist in Pre-glacial 

 times and had been foimd in the Middle Glacial period. Mr. Prestwich found 

 the tooth of one near Bricket "Wood. 



With regard to the question of the timber depending on the soil, he thought 

 that the author of the paper appreciated the possibility of the fine growth of beech 

 on a chalky soil. There was one thing about the dependence of the tiiuber on the 

 soil. It would generally be found that where the beds of London Clay were seen 

 overlpng the Chalk, the district was distinguished by the luxuriant gi-owth of 

 trees, and from that it could be predicted where such an outlier was to be found. 



As to the sanitary influence of the drifts, he was a little doubtful how far they 

 were advantageous to health, and how far the air of Hertfordshire could be re- 

 garded as being so very valuable that a house there was worth so many years' 

 purchase ; for he was afraid that in some of the valleys the consumption death- 

 rate was almost greater than in other parts of England, especially where, regardless 

 of all ideas of sanitary science, the houses were built within a foot or a foot and a 

 half of the ordinary water-level. He believed that there was more done in 

 promoting the increase of consumption by injudicious building on improper sites 

 than by any other means. But there was another idea, the possibility of obtain- 

 ing water from shallow wells. Shallow wells, where there were only one or two 

 people living in the neighbourhood, were not bad sources of supply ; but where 

 there was a village on a Tertiary outlier or the boulder-clay — where there were 

 some gravels, and houses congregated around the supply of water, and no attempt 

 was made at a proper system of drainage, he could not think that the results were 

 so much to the credit of the drift deposits as the author of the paper seemed to 

 think. 



With regard to Dr. Brett's question as to the date of the earliest appearance of 

 man. Dr. Brett was qiute right in sapng that it was a matter for discussion. 

 Some geologists had admitted that man might have existed in I're-glacial times, 



