Geological Society of London, 89 



called "middle-glacial" gravels and sands, to account for tlieir oc- 

 currence in certain areas, and their non-occurrence in others, where 

 they might reasonably have been expected. Also to describe a series 

 of gravels of doubtful age and origin in the Cambridge valley. 



A short description of the geology and physical features of the 

 district was given, and an inference drawn, from the varying faunas 

 of the "Crag," that the land was sinking during that era and until 

 after the deposition of the Cromer " Forest-bed." Then Arctic con- 

 ditions began to prevail, and the great glacial subsidence com- 

 menced ; the "lower glacial" beds were formed, and succeeded by 

 a large series of false-bedded gravels and sands, with intercalated 

 patches of unstratified clay. These deposits run up only to a certain 

 level, about 300 feet, never quite reaching the top of the Chalk 

 escarpment, where the overlying Boulder-clay is invariably found 

 resting on the older rock, without any gravel or sand between. The 

 author inferred from this circumstance that after the deposition of 

 the " lower " beds, and as submergence went on, the waters of the 

 North Sea were again united to those of the Atlantic. A strong 

 current was thus set up, which swept down from the north, bringing 

 with it the material of which the gravels are composed, and which 

 is found to consist of pebbles, all derived from the northern and 

 eastern coasts, mixed with flints from the Chalk. The escarpment 

 of this formation stood at the time above the water, but when once 

 sufficiently submerged to admit the water over its lower portions, 

 the conditions were altered, the current lost its force, and the de- 

 position of gravel ceased. An occasional iceberg had dropped its 

 load of unstratified clay, which became intercalated with the gravels, 

 but the greater number of such bergs were quickly swept away to 

 the south. Now the waters had access to a larger area, the formation 

 of gravel was succeeded by that of Boulder-clay, which in the 

 author's opinion is entirely composed of masses of clay inclosing 

 boulders, brought down and dropped by icebergs in mass, which 

 accounts for its want of stratification. 



This Boulder-clay rests evenly on and at the higher level overlaps 

 the "middle-glacial" sands; it then caps the Chalk escarpment, and 

 plunges down into the Cambridge valley, even to the present level 

 of the sea ; but in no instance on or beyond the escarpment does any 

 sand or gravel intervene between it and the older geological for- 

 mations, although just over the scarp (on the south side) the gravels 

 run up to an elevation of 300 feet. The gravel-forming currents 

 were evidently confined to the seaward side of the Chalk range, 

 and excluded from the Cambridge valley, which is undoubtedly pre- 

 glacial, and which formed at the time a large inlet, land-locked on 

 every side but one, discharging its waters through the opening now 

 occupied by the estuary of " The Wash." 



In the Cambridge valley there are sheets of river-gravel of recent 

 date, some patches of doubtful age, but not traceable under the 

 Boulder-clay, and an elongated series of gravels at a level of 20 to 

 60 feet above the present level of the Cam. These are in some parts 

 distant from the present course of the river, and present a striking 



