EAST A2JGLIA DURING THE GLACIAL PERIOD. 201 



the conclusion that, strictly speaking, there are no Lower or Middle 

 Glacial deposits within the area of the Cambridge valley *. 



Supplementary Notes. 



Since the above notes and the conclusions therefrom were brought 

 before the Society, the completion of the mapping of some of the 

 gravels, mentioned as of doubtful age, seems to have thrown light 

 upon the date and mode of their formation. It has afforded, also, 

 additional evidence in support of the theory advanced respecting 

 those gravels which were thereby asserted to be relics of an ancient 

 river Cam. 



There is a hill called " The Eivey," situated about ten miles S.E. 

 of Cambridge ; its height above the Cam is about 325 feet ; it is, as it 

 wore, an outlier from the escarpment, and it is similarly covered by 

 Boulder-clay. This Boulder-clay rests directly on the Chalk, and is 

 capped by a few feet of gravel ; it is supposed that this is a patch 

 of " Denudation gravel," and that the Boulder-clay beneath it re- 

 tains its full thickness ; or it may be a higher example of those to 

 be described. In a direction running away from the escarpment 

 are patches of gravel at a level several feet lower ; then, further on, 

 other patches at a still lower level, and others, still further away, 

 with less elevation, the Boulder-clay being continuous beneath them 

 all. At Hildersham, in the valley, 1| mile from the Eivey and 

 200 feet below the summit of the hill, the gravel and Boulder-clay 

 occur in the same relative positions ; and a little further on, the 

 gravel overlaps the clay and rests on the Chalk. 



This interesting and well-marked geological feature has been pre- 

 served, it may be, by its position in the bend to the north of the escarp- 

 ment ; and it affords a key to many other patches of gravel in similar 

 positions, and heretofore considered as of doubtful age (p. 200). 

 All the patches (many of which are small), and the indications of 

 several other patches removed by recent denudation, seem to form 

 parts of lines that once were continuous, and which are more or 

 less at right angles to the long series ascribed to an old course of 

 the Cam. They continue in a gradually descending order from 

 almost the top of the 'scarp down to the level of that series — that 

 is, from 325 feet down to 20 feet above the present river. 



The explanation proposed is, that the slope of the Preglacial 

 'scarp was entirely covered by Boulder-clay, that the valley was, in 

 fact, almost filled by that deposit, the patches of Boulder-clay which 

 here and there remain marking out the line of that Preglacial 

 escarpment (see ante, p. 198). This Boulder-clay has been removed 



* Since the above paper was read the author's attention has been called to 

 the fact that in the ' Geological Magazine ' for February 1870, Mr. S. V. 

 Wood, Jun., publisbed a statement to the effect that the Middle Glacial beds in 

 East Anglia do not occur at a greater elevation than 250 feet ; also, that in a 

 section illustrating a paper by him read before the Society, June 19, 1867, the 

 overlap of those beds by the Boulder-clay, and the occurrence of the latter in 

 the Cambridge valley without any Middle Glacial are represented. Although 

 Mr. Wood did not draw the same inferences from these facts, he is entitled to 

 priority in their observation. — W. H. P. 



