IN THE GLACIAL DKl'OSITS AT HENnON. 581 



an excavation extending to over 00 feet has been raade, exhibitinj^ 

 the conditions witnessed in fig. -i. Towards the north end of tli(; 

 pit B, the floor was seen to rise uj) rather suddenly, and the sand 

 and gravels diminished to a few feet. Towards the south end a mass 

 of BouLler-clay, about 12 feet across, dipped down suddenly till it 

 rested on the underlying Londoji Clay without the intervention of 

 any sand or gravel. Between these points there was an average 

 thickness of (> to 7 feet of more or less well-stratified sand and 

 gravel, and at the base, resting on the Loudon Clay, were several 

 masses of sarsen-stone, 2 to 2| feet in length. The lower gravel 

 also contained, scattered about in it, several large angular masses of 

 sarsen-stone, large but slightly-worn fiints, and sometimes masses 

 of a brown-clay much resembling the underlying London Clay. On 

 the westward slope, at a distance of about 150 feet from this pit, 

 and some 25 feet lower in horizon, another pit (C) was opened. 

 Here it was found that the lower rough gravels, which averaged 

 about 4 feet in the upper pit, were greatly diminished in thickness, 

 and were replaced by clean white sand, the beds above being on 

 the whole almost identical with those iu the upper pit. A. wide 

 depressed mass of the Upper Boulder-clay was also found to come 

 in at the south side of this pit. In some deep drains, which were 

 made for the ])urpose of carrying away the water from these pits, 

 similar varying conditions were witnessed *. It will be seen, there- 

 fore, that these Glacial deposits do not, as has been usually supposed, 

 merely rest on a plateau of the London Clay, but they lie on a very 

 irregular surface and descend everywhere along slopes of previously 

 formed depressions and valleys in the London Clay. I have care- 

 fully traced the sections along the slopes, and I find that there is 

 sometimes a difference of at least a hundred feet from the highest 

 point at which London Clay has been touched on the ridge, to that 

 in which it is found underlying almost identical sections on the 

 slopes. 



III. Distribution of the Glacial Deposits. 



On the accompanying map (PI. XXII.) I have outlined the 

 margin of the deposits, so far as they have been made clear through 

 pits and in sewering the district, and I have indicated some of the 

 spots where the deposits have been well exposed. It will be 

 observed that tlie ])atch occupies an area more than three times the 

 size of that shown in the Geological-Survey map of surface deposits. 

 Many years ago I mentioned to Mr. Whitaker and to Mr. Horace 

 B. Woodward that the deposits extended beyond the limit shown, 

 and in the recent excellent Memoir of the Geological Survey they 

 have fully referred to the facts I then communicated to them. 

 Much additional evidence has, however, been since obtained, and the 

 boundary has been further extended. The nature and contents of 



* A test-bole was recently dug at the bottom of this field, about 65 feet 

 below the horizon of tlie upper pit, and similar sand and gra\el was met witb, 

 covered by about .'i tVet of Boulder-clay. Hei-e more ' race ' was found in tho 

 clay than in the excavations higher up in the field. 



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