Maw — Relative Ages of the Boulder-clays. 



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sand, silt, and clay beds (a.); the sandy or 

 gravelly pervading over the clayey character 

 in its upper part. The Boulder-clay on the 

 high ground (c) has a range of from 150 feet 

 (its base) to 220 or 230 feet above the sea, 

 generallj'^ resting on a bed of sand and gravel 

 (d) between which and the overlying clay 

 there is little or no gradation or interstrati- 

 fication. The Boulder-clay itself, compared 

 with that on the coast, is, throughout its 

 mass, remarkably uniform in this character, 

 and even in colour, generally free from sand 

 beds. It is made up of clay and chalk detri- 

 tus, and some transported materials, smaller 

 and more even in size than the foreign mat- 

 ter of the coast Boulder-clay (a b), and re- 

 markably uniform throughout the whole of 

 its geographical distribution. The low-level 

 Boulder-clay also seems to maintain its cha- 

 racter through a wide geographical range, 

 graduating upwards from very tough blue 

 clay at the sea-level, into contorted silty and 

 sandy beds, both on the east, as well as the 

 west coast of England and Wales. I mention 

 these facts rather fully to show the proba- 

 hility of the distinction and difference in age 

 of the two deposits, and that each maintains 

 a certain amount of uniformity of character 

 and position. Mr. Searles Wood, jun., has 

 fully recognised this, and assumes an order 

 of succession from the lower to the higher 

 clay, the latter of which he considers the 

 more recent. This seems to rest on evi- 

 dence not very definite, and I wish to sug- 

 gest the possibility of another order of se- 

 quence, as affording an explanation of much 

 that is otherwise difficult to understand, and 

 as being quite as consistent with the ob- 

 served facts, viz., that the Boulder-clay on 

 the higher level is the more ancient, that on 

 the coast having been deposited after its 

 partial denudation. With respect to the 

 difficulties that are opposed to Mr. Wood's 

 views, one of the most prominent seems to 

 be the analogy that may be drawn between 

 the relative age of high and low-level river 

 gravels and the relative age of the higher 

 and lower Boulder-clays. In the case of 

 river gravels, that on higher levels is ge- 

 nerally admitted to be the more ancient, 



