BRITISH POSTGLACIAL e^ RECENT DEPOSITS 417 



large fall of sandstone took place, and the course of the stream 

 was altered in the manner already described. A new course 

 having been opened out — a process which must have occupied 

 considerable time — wetter and colder conditions of climate 

 ensued, snow-fields accumulated, and a local glacier occupied 

 the glen, following the new course formed by the stream, but 

 never attaining a sufficient size to plough down and clear away 

 the bergfall. 



The local glaciers which existed in postglacial times, that 

 is to say, during the accumulation of the deeper and older 

 deposits of Carse-clay and the formation of the 45-5 0-feet raised- 

 beach, probably lingered in some valleys till the sea-level had 

 fallen to the 25-30-feet level. But the beaches and Carse-clay s 

 of this lower level approximate so closely in character, and in 

 the nature of their organic remains, to the beaches which are 

 now in course of formation, that the temperature of the Scottish 

 seas at the time the waves washed the 25-30-feet level may be 

 supposed not to have differed much, if at all, from that which is 

 experienced at the present day. That the sea stood at that 

 level for a considerable time may be inferred from the amount 

 of work it was able to perform. Broad platforms have been 

 hewn in strata of sandstone and other and often harder 

 rocks which formed the sea-margin ; cliffs have been cut back, 

 and considerable caves have been hollowed out at their base by 

 the action of the breakers. Sometimes the old beach consists 

 of only a more or less narrow ledge sawn into the face of a steep 

 rock-slope or cliff, and showing old sea- worn stacks and hollows, 

 at other times it forms a wide flat, two or even more miles in 

 breadth. It is upon these beaches that the greater number of 

 the Scottish seaports and fishing -villages stand. The lower 

 reaches of the great estuarine flats of the Tay, the Forth, the 

 Clyde, the Nith, and others, all belong to the period of the 

 25-30-feet beach-level, but owing to the working of the rivers 

 it is often difficult in such regions to distinguish between the 

 deposits of the 45-50-feet beach and those of later age. The 

 large rivers in their many windings have ploughed down through 



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