CLOSE OP POST-PLIOCENE ADVENT OF MAN. 287 



Further, as the land rose, its surface was greatly 

 and rapidly modified by rains and streams. There 

 is the amplest evidence, both in Europe and America, 

 that at this time the erosion by these means was 

 enormous in comparison with anything we now ex- 

 uerience. The rainfall must have been excessive, 

 the volume of water in the streams very great; and 

 the facilities for cutting channels in the old Pliocene 

 valleys, filled to the brim with mud and boulder-clay, 

 were unprecedented. While the area of the land 

 was still limited, much of it would be high and 

 broken, and it would have all the dampness of an 

 insular climate. As it rose in height, plains which 

 had, while under the sea, been loaded with the 

 debris swept from the land, would be raised up to 

 experience river erosion. It was the spring-time of 

 the Glacial era, a spring eminent for its melting 

 snows, its rains, and its river floods.* To an ob- 

 server living at this time it would have seemed as 

 if the slow process of moulding the continents was 

 being pushed forward with unexampled rapidity. 

 The valleys were ploughed out and cleansed, the 

 plains levelled and overspread with beds of alluvium, 

 giving new features of beauty and udility to the land, 

 and preparing the way for the life of the Modern 

 period, as if to make up for the time which had 

 been lost in the dreary Glacial age. It will readily 

 be understood how puzzling these deposits have 



* Mr. Tyler has well designated this period as the Pluvia.1 

 age. Journal of the Geological Society, 1870. 



