Page:Quarterly Journal of the Geological Society of London, vol. 32.djvu/275

Rh If the explanation offered be the true one, we have here a series of river-gravel terraces occurring at all heights, from nearly the bottom of the present valley up almost to the top of the Chalk escarpment.

Fig. 1. Map of a part of East Anglia, showing the Drift-deposits. Scale 8 miles to 1 inch.

2. Section from London-Clay escarpment to the Cambridge valley along the line indicated on the map. Horizontal scale 4 miles to 1 inch; vertical scale 800 feet to 1 inch.

Prof. said that his impressions, formed twenty years ago, agreed with those of the author. It was a very simple case of geology complicated by geologists. He inquired whether the author thought that such valleys as extend up to the Chalk from the German Ocean were excavated before the Glacial period, or whether they were then filled up and afterwards excavated. He also asked whether the author was quite satisfied that all the gravels are waterworn by tidal action. It seemed to him exceedingly interesting to find that Mr. Penning pushed the ice-cap a little further back.

Prof. Morris remarked that the valley of the Cam presents two or three different conditions; near Cambridge the river flows over the Gault, cutting through the old gravel between Barnwell and Chesterton. The valley was probably excavated in the Boulder-clay, which occurs at higher levels, and once no doubt covered the whole district.

Mr. thought that the Boulder-clay did fill the valleys, and that the boulders referred to by the author had been derived from the Boulder-clay. One point of special interest in the paper seemed to him to be that the author regarded the whole Glacial series as continuous, in opposition to those who would place the excavation of all the valleys in the Glacial period, while the author considers them preglacial. At Cromer the so-called Middle Glacial is nothing but blown sand.

Mr. inquired as to the order of sequence of certain beds known as Lower, Middle, and Upper Glacial, what evidence