Maiv — Relative Ages of the Boulder-clays. 99 



and there seems no substantial reason why the same sequence should 

 not hold good with respect to the Boulder-clays. 



Again, another difficulty, Mr. Searles Wood at p. 4 of his remarks 

 in explanation of the map of the upper Tertiaries, says, " The 

 Chillesford beds described by Mr. Prestwich, in 1849, as over- 

 lying the Eed or Coralline Crags, pass up without the least break into 

 the Middle drift, (n Fig. 1) and are evidently part of that division." 

 Although the evidence on this point is scarcely decisive, I think 

 the probability of the view taken by Mr. Wood is very strong. 

 The bed Mr. Wood describes as " Middle drift," is the gravel under- 

 lying the high-level Boulder-clay (d. Fig. 1), and separating it 

 from- the Chalk, or in some cases from the intervening Norwich 

 Crag. As far as my observations go the Chillesfoi'xl Clay, both 

 in Norfolk and Suffolk, is really part and parcel of the Upper 

 Norwich Crag. In the well-known Crag-pit at Chillesford, 

 this bed, containing deep sea Arctic shells (which at Norwich is 

 almost immediately superimposed on the true Fluvio-marine Crag, 

 both occurring at the base of the beds corresponding with the Chil- 

 lesford Clay), lies in the midst, towards the base, of the Chilles- 

 ford Loam and Clay ; as the Boulder-clay Till of the Norfolk and 

 Suffolk coast is unquestionably superimposed on the Norwich Crag, 

 a difficulty at once presents itself in endeavouring to interpolate 

 it in the Suffolk series leloio Mr. S. Wood's "Middle-drift." I 

 know it has been assumed that the Chillesford beds are the repre- 

 sentatives of the coast Boulder-clay, but there is nothing in its 

 physical character, the thickness of its mass, or condition of its 

 fossils, to support such an identification. At page 6 of Mr. Wood's 

 paper, the difficulty in question seems to be recognized, and involves 

 a statement of the hypothetical possibility of the Eed Crag being 

 newer than Mr. Wood's Lower-drift (or Coast Boulder-clay, a. and 

 B. Fig. 1). 



I believe there is no evidence of the direct superposition of the 

 high-level Boulder-clay on that of the coast. If the higher clay 

 was more recent than the lower, surely some cases would occur 

 in which direct superposition was evident. But there is no coast 

 section exhibiting the sequence of the high level directly over 

 the low-level clay, with the intervening sand bed ; there are very 

 many instances of the coast Boulder-clay being capped with gravel, 

 and of the Boulder-clay of the high ground being superimposed on 

 a subjacent gravel bed ; it must be admitted that these gravel beds 

 correspond in height, and in many cases present the appearance of 

 continuity, but proof of their identity seems to be wanting. 



The Boulder-clay of the high ground of the Eastern counties, with 

 its subjacent gravel-bed, presents much evidence of great antiquity : 

 as has been shown by Mr. Salter and Mr. Wood, it has been ex- 

 tensively faulted with the Chalk, and it partakes of the general 

 denudation contour of the country, most of the principal river- 

 valleys having been cut through it deeply into the Chalk and 

 Oolite. The small outlier at Muswell Hill (d. Fig. 2) appears to be 

 the remnant of a more extensive deposit, the denudation of which 



