Wood and Ilarmer — Geology of Nor^f oik and Suffolk, 455 



breaking from the Glacier and grounding, picked up masses of the 

 marl forming over the sea-bottom in that part of the area. These 

 masses the bergs carried out into the area where the brick-earth was 

 accumulating, and grounding again, imbedded them in the brick- 

 earth, and even in the subjacent Till and Weyboume Sand, contort- 

 ing the beds in the process. From detached portions of this marl, 

 which they have found as far south as Claydon, near Ipswich, and 

 Stanstead, near Lavenham, in Sufiblk, they infer that this deposit 

 covered the west of Suffolk and Norfolk, but underwent great denu- 

 dation in the former part by the waters of the Middle Glacial sea, 

 the sands of that sea, west and south of Diss, lying up to bosses 

 of it in some parts, and overlying it in others. 



That the fauna of the lower Glacial beds is marked by the disappear- 

 ance of all except the boreal and arctic mollusca of the Crag, rather 

 than by the introduction of a new fauna, the principal introduction 

 being the Tellina solidula. A list of 28 species of mollusca was 

 given by the authors from these lower Glacial beds. 



That the sands and gravels, attaining frequently a thickness of fifty 

 or sixty feet, which underlie much of the great Boulder-clay in the 

 six counties before-mentioned, and which, termed by the authors the 

 Middle Glacial, pass over the Lower Glacial series, a, b, c, and d, just 

 described, contain a molluscan fauna of which they enumerate 23 

 species. The interest attaching to this fauna consists in the fact that 

 Pedimculus glycimeris, which dies out in the newer part of the Red Crag, 

 and is excessively rare in the Fluvio-marine or true Norwich Crag, re- 

 turned during this formation in abundance, as well as Ostrea edulis, a 

 shell which similarly disappears in the newer beds of the Crag, and 

 it is not known now within the Arctic circle. Although a bed, a few 

 feet thick, of Boulder-clay identical in composition with the great 

 Boulder-clay, but of very limited extent, occurs at the base of this 

 formation at two places in north-east Suffolk and at one place in 

 Hertfordshire, its features and faima both appear to indicate that 

 some considerable amelioration of the very severe climate to which 

 the marl of the Contorted Drift that preceded it was due, occurred 

 in the interval occupied by this formation. 



That the true wide-spread Boulder-clay of the east of England, 

 termed by the authors, the Upper Glacial, ceases from denudation 

 in northern Norfolk, along a line drawn from Winterton on the 

 north-east coast to Norwich, and thence passing near Aylsham 

 through Cawston, Guestwick, and Barney, to a point a little north 

 of Fakenham. On the east of the county, that is to say, to the 

 south-east of a line joining Norwich and Happisburgh, the Middle 

 Glacial sand and the underlying contorted Drift crop out from 

 beneath the true Boulder-clay, in regular sequence ; but over the 

 centre of Norfolk the authors describe a very anomalous structure, 

 which is that the true Boulder-clay (or Upper Glacial) has been de- 

 posited in a great trough more than twenty miles wide, which has 

 been excavated through the Middle Glacial sands and subjacent 

 Lower Glacial beds down to the Chalk. The effect of this has been to 

 bring the true Boulder-clay (or Upper Glacial), resting on the Chalk, 

 down to a level on the west and south-west of Norwich, which in 



