5 and 6. Thus, for instance, on the Cromer coast, we find the former most deeply and irregularly indented by troughs filled with the base of 5, both deposits being there in much greater thickness than in the case before us ; while in the inland sections we find it rising through 5 in bosses of greater or less extent, the Boulder-clay (6) being spread there over it and over 5, sometimes resting on the one and sometimes on the other, thus showing 4 to have formed either islands or shoals in the Middle Glacial sea.
The intraglacial denudation of the Tare valley, disclosed by the sewer-works, serves to explain a feature brought before the Society by one of us in 1866*. In that case a bed of Boulder-clay was shown lying in the bottom of the Yare valley, and described as a third Boulder-clay. Although, at the time, we both regarded it as distinct from the great Boulder-clay (6), we now incline to think that the bed in question is either the bed a, or else merely the Boulder-clay 6 brought down into the bottom of the valley by a repetition of the denudation which, we have just seen, commenced after the deposit of the contorted drift 4. The dotted lines in our section represent probably the way in which 5 bent down into this hollow of denudation ; and it seems to us that the denudation was renewed after the deposit of 5, sweeping out so much of that bed as had been deposited in the hollow, but leaving it in the hole or trough which is shown in our section, and thus allowing 6 to be thrown down upon the chalk direct, as shown in the section referred to†.
In the adjoining valley of the Wensum a somewhat similar state of things has occurred, as we have found there the Middle Glacial sand (5) overlain by the Boulder-clay (6) in a hole in the chalk, and resting directly upon it, below the level of bed 3, which, in that part, forms the general base of the formations superior to the chalk, and constituting the solid mass of the country.
No infiltration or slipping can explain these features, because the blue clay (a of the accompanying section) is not, so far as any of the pits around disclose, present in the neighbourhood, and because the deposits which underlie the beds in question, when in their usual position, do not occur beneath them when thus abnormally placed, although, in the case of the blue clay a, we ought to add that the shafts do not reach its base, so that it is unknown whether anything intervenes between it and the chalk.
In conclusion, we would venture to remark that the sections referred to appear to us to militate against the excavation of our East-Anglian valleys by river-agency, as well as to show the illusory character of the level-test as applied to the elucidation of the age of the newer Tertiaries, especially of those occurring in valleys ; although we are far from saying that the evidence of level, when kept in due subordination to other features, has not its value.
Note. — This paper was postponed in the hope that the progress of the works would have brought further facts to light ; but nothing
- Quart. Journ. Geol. Soc. vol. xxiii. p. 89.
† Ibid. See the bed a of that section, which is not to be confounded with the bed a of the section which accompanies the present paper.
