112 S. V. WOOD, JTTN., AND F. W. HARMER ON THE 



these altitudes and down to the sea-level, would at first sight make 

 it doubtful how far this limit to the submergence is a sufficient ex- 

 planation of the mode in which the deposit is distributed. One 

 circumstance, however, seems to corroborate it, which is that the 

 Middle Glacial gravel at Finchley is largely made up of pebbles 

 derived either from the pebble-beds associated with the contiguous 

 Lower Bagshot outliers of Essex or from those beneath the London 

 Clay ; and we must suppose that those sources were above water at 

 the time, in order to supply the pebbles, as these do not appear to 

 have been introduced by the action of glacier ice. The highest of 

 any of these sources does not attain an elevation exceeding 440 feet ; 

 and most of them only reach elevations nearly 100 feet less than this, 

 and not much exceeding that of the Middle Glacial itself at Finchley. 

 If, however, this limit to the submergence during the accumulation 

 of the Middle Glacial was the case, we should regard it as an indica- 

 tion that, so far from the glacial submergence having been an unin- 

 terrupted one, an emergence must have succeeded the Contorted 

 Drift, because, the entire thickness of the Lower Glacial deposit 

 around Cromer having itself exceeded 200 feet, there must have 

 been far more than 200 feet of water over it in order to trans- 

 port the bergs which, in grounding, have deposited such great 

 masses of Marl in that Drift, contorting it in the process. Some of 

 these masses are so enormous that it is hardly possible to suppose 

 that a berg capable of transporting one could have grounded in much 

 less than 1000 feet of water*; so that it seems to us that when 

 these masses were thus introduced, Northern Norfolk had undergone 

 a submergence far beyond what is thus supposed to have prevailed 

 during the accumulation of the Middle Glacial. One of these masses 

 forms the entire cliff a short distance west of Woman -Hy the Gap ; 

 and this it was our fortune once to see nearly free from the usually 

 obscuring talus ; and it seemed to be about 300 yards in length by 

 60 feet in height. Its breadth, of course, was concealed. 



It is clear that these introductions took place before the formation 

 of the gravel overlying the Contorted Drift in the Norfolk cliff — 

 because the line of denudation dividing this drift from the overlying 

 gravel is clearly defined, and cuts across the Drift and its included 

 masses indiscriminately. 



If, therefore, the land rose after the formation of the Contorted 

 Drift to such an extent that during the"; deposit of the Middle 

 Glacial the depth of water did not exceed 400 feet, we need not 

 hesitate to suppose that it emerged altogether, and that the Lower- 

 Glacial sea-bottom was converted into land, if other features, such 

 as that indicated possibly by section XVIII. at Starston, and the 

 excavation of valleys through this sea-bottom, with the formation in 

 them of the interglacial bed of the Yare valley, point in this 

 direction. 



* Bergs of great dimensions which have acquired a pinnacled form, and 

 therefore spread out under water with a wider base, float in a much less depth 

 of water than those of tabular form ; but, before they had time to acquire that 

 shape, they would probably have parted with the freight of marl carried at their 

 bottoms. 



