182 SIR JOHN" . EVANS — THE STONE AGE 



With a severe climate, also, ground-ice and sliore-ice, both of 

 which have considerable transporting power, would be formed ; 

 the rocks would be disintegrated by frost, and the fragments or 

 talus formed would be easily carried away by the streams. 



There is also another reason why we have these valleys formed 

 in Chalk districts. Rain-water is enabled to dissolve chalk by 

 becoming charged with carbonic acid from the decomposition of 

 vegetable matter on the soil on which it falls, and from eveiy 

 square mile of chalk country no less than 140 tons of chalk are 

 carried away in solution each year by the water which percolates 

 through the chalk, thus eventually lowering the surface of the 

 country. 



The fact that the constituent parts of the drift gravels con- 

 taining Palaeolithic implements are always of the same petrological 

 character as are the rocks in the existing river -basins, proves that 

 the gravels are due to some local cause ; and that they frequently 

 contain land and fresh-water shells and mammalian bones of the 

 Quaternary period, is conclusive evidence of their fresh-water 

 origin. The character of the beds and their manner of deposition 

 also exactly accord with the river hypothesis ; and, moreover, they 

 occur in such positions as might have been expected had their 

 presence been due to the action of a stream excavating its valley 

 in the manner I have described ; indeed, in several instances the 

 probability that certain gravels contained Palaeolithic implements 

 was pointed out before implements were actually discovered in 

 them. There are other points of agreement between the actual 

 phenomena and those of such river-action as I have supposed to 

 have taken place, and we may, without any doubt, accept the 

 implements as being truly characteristic fossils of the deposits in 

 which they are found, and these as being Quaternary river-deposits. 



Some important discoveries of Palaeolithic implements have 

 recently been made in the gravel in the valley of the Colne by 

 Mr. Clouston, a resident at Watford, whom I am pleased to see 

 here this evening. As the gravel in which he has found them 

 is 40 feet above the level of the existing river, it follows that at 

 the time this gravel was deposited the bed of the river was at that 

 height above its present level. 



In the valley of the Gade discoveries of Palaeolithic implements 

 have been made by myself. One implement was lying on the 

 surface of a ploughed field near Bedmond, at a spot which, though 

 probably 160 feet above the level of the nearest part of the river, 

 is nearly at the bottom of one of the lateral valleys leading into 

 the main valley of the Colne between Boxmoor and Watford. The 



