FOSSILIFEROUS BOULDER-CLAYS. 



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rated striae, while many retain no signs of ice-action. Differing in texture, they are often 

 loose and rubbishy — sandy and earthy — and to a large extent have been exposed to the 

 wear and tear of air and water. 



They sometimes contain blocks even larger and heavier than those in the lower clay ; 

 but these blocks may have been dropped into the bed by floating ice. 



1. — Some of the beds of this series consist of a thick clay with many boulders, and on 

 a cursory examination might easily be mistaken for " Boulder Clay " in the sense in which 

 we have employed the term. They may be distinguished, however, by observing that the 

 included stones while often angular and subangular, have a feeble polish, and preserve 

 only faint reminiscences of their former striations. Generally speaking, also, the clay and 

 the boulders are far less compactly pressed together, and are not welded, like the old 

 Boulder Clay, into an almost solid mass. 



Sometimes a shell bed may be seen intervening between an upper bed of this 

 kind and a lower Boulder Clay ; and at other times the two clay beds may be seen 

 in contact, the shell bed having been eliminated. 



During some excavations at Chappel Hall, near Airdrie, the following sections were 

 exposed within seven yards of each other 



ft. in. 



Upper clay with boulders . . . . . 14 0 



Finer clay, containing smaller stones, with TeUina calcarea and Ci/jjriiia 



Islandica ; in the deepest part (but rapidly thinning out) . 2 1 



Boulder Clay, not pierced. 



At seven yards' distance the shell bed disappeared and the two clays met. 



Upper clay with boulders . . . . .53 



Boulder Clay, not pierced through . . . .96 



We carefully examined these two clays, and found the distinctions between them very 

 decidedly marked. The boulders in the lower bed were polished with extreme fineness, 

 and the striations upon them were numerous and clear, but in the upper bed only a few 

 stones had slight indications of %ix\m, while many had the appearance of having been 

 worn down. The upper clay was also looser and more easily worked than the lower. 



2. — Other beds of this series are composed of sand and gravel rather than clay, and 

 are either unstratified or very rudely stratified, and often contain angular and 

 imperfectly stratified boulders. 



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