GEOLOGY OF THE PORTESHAM DISTIIICT. 195 



Monument. On the western side of this eminence great masses of 

 flints, cemented together by a silicious matrix, are scattered here 

 and there upon the plateau. With some of them the Dolmen, 

 called the Hellstone, has been constructed, around which many 

 boulder-like masses lie. There is a great trail of them in a comb 

 to the north called Bride Bottom, recalling to mind the Marl- 

 borough wethers ; and there are numbers of them in the valley to 

 the south in the street of the village of Portesham. These 

 boulder-like masses many of them weigh many tons are 

 clearly the remains of a former extension of the tertiaries, which 

 the denuding agency, whatever that was, found too massive to 

 remove. 



It must have been before the removal of the tertiary gravel that 

 the pot-hole was formed where the worked flints were found. The 

 present exposure is on the steep side of the narrow valley, down 

 which runs the road from Winterbourne, and is close to the 532- 

 foot bench mark on the six-inch map. The pot-hole is exposed in 

 a section about 40 feet high, in the steep side of the down, which 

 consists of lower chalk, devoid of flints. Consequently the flints 

 which fill the pot-hole cannot have been derived by solution 

 of the chalk in situ. Moreover, their peculiar character proves 

 that they once formed a portion of the tertiary gravel of the 

 district. 



Seeing that a pot-hole, or pipe, is due to the percolation of 

 water, it cannot have been formed on a steep slope. We are 

 carried back, therefore, to a far distant time, before this valley 

 was eroded, and when the chalk had a level surface covered by 

 a spread of tertiary gravel. 



Such pot-holes are natural museums in which relics of the old 

 covering are preserved. In the neighbourhood of Dorchester, on 

 bare chalk hills, we find them filled with tertiary clays and sands. 

 Near Lenham, in Kent, they contain remnants of pliocene 

 fossils. 



There does not seem, however, any reason to believe that these 

 worked flints were originally part of the contents of the pot-hole, 



