100 



Maw — Relative Ages of the Boulder-clays, 



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s-s 



2nd. 



3rd. 



accompanied the excavation of the Thames 

 valley. Now, if Mr. Dawkins' view is cor- 

 rect, that the Brick-earths and gravels oc- 

 cupying this valley are overlain by a later 

 glacial deposit, the question at once sug- 

 gests itself whether this can be more pro- 

 perly identified with the high-level clay 

 of Suffolk, or the low-level Glacial depo- 

 sits that occur at its own level along the 

 coast. If it cannot be identified with, the 

 coast clay, you have, on Mr. Wood's views, 

 the complicated difficulty .of three distinct 

 Boulder-clays of diiferent ages. 

 1st. Mr. Wood's ''Lower drift," or coast 

 Boulder-clay. 



Mr. Wood's "Upper drift," sepa- 

 rated from the first by clean gravel 

 beds, ("Middle drift"). 

 The glacial beds of Mr. Dawkins', 

 overlying the beds that were depo- 

 sited in the Thames valley, the ex- 

 cavation of which, appears more re- 

 cent than the deposition and partial 

 denudation of the Muswell Hill 

 Boulder-clay (d Fig. 2) which pro- 

 bably corresponds with Mr. Wood's 

 " Upper drift," or high-level clay. 

 I do not mean to say that such a series 

 of deposits during the Glacial period is 

 impossible, but, without any direct evi- 

 dence to the contrary* it seems preferable 

 to take the simpler view, viz., that the 

 beds of the Thames valley, containing 

 transported materials, may be an inland 

 extension of the Boulder-clay on the same 

 level, fringing the coast, and that both of 

 these were deposited after the deposition 

 and partial denudation of the Boulder- 

 clay on the higher ground. 



Another point to be noticed is a fre- 

 quent terrace-like structure of the Boulder- 

 clay, fringing the coast, running straight 

 inland till it meets with rising ground of 

 older formation, against which it termi- 

 nates as though its general level was the 

 original surface of deposition ; this charac- 

 ter is not confined to any particular part 

 of the coast, but presents itself, on both the 

 east and west, wherever Boulder-clay oc- 

 curs on the coast. Now if the Boulder- clay 



