part 1] AT LITTLE HEATH, BEftKHAMSTED. 49 



from the Lower Greensand, had also passed through a Reading- 

 Bed stage. Mr. Osborne White (in a paper published in the Proc. 

 Geol. Assoc, vol. xix, 1906, p. 371) had described a section in the 

 Reading Beds at Lane End (Bucks) which yielded these pebbles in 

 abundance, and it was quite possible that from strata of this age 

 once existing farther north but now destroyed, the small quartz- 

 pebbles so common in the Drift-gravels north of the Thames had 

 come. This might also explain the presence of the quartz-pebbles 

 forming part of some sarsens. Sarsens, being portions of the 

 Reading Beds hardened in their original position, would naturally 

 partake of the character of the strata at the spot where the 

 hardening process took place. 



Sir Henry Howobth expressed the opinion that Mr. Gilbert's 

 paper contained a large store of facts carefully observed and of in- 

 ferences. Substantially the paper describes a section on the Chiltern 

 plateau, in which two beds of stratified sand and gravel respectively 

 are overlain by a bed of heterogeneous and unstratified clay with 

 pebbles. In regard to the former beds, he considered that a very 

 good case had been made out for their Middle or late Tertiary age, 

 and for their correlation with similar deposits of similar partly- 

 denuded beds north of the Thames. The absence of fossils is a 

 common occurrence at this horizon ; the so-called 'barren sands' of 

 the Red Crag are well known, many stretches of gravel of that date 

 are without shells, and it was difficult to suggest any age for the 

 beds in question other than Tertiary. The speaker had discussed 

 similar beds south of the Thames at some length in his ' Ice & 

 Water,' vol. ii. pp. 159-75. In regard to the unstratified clay- 

 with-pebbles, he objected to the use of the term glacial as applied 

 to this and similar beds. There was not a single glacial feature 

 about them. All the pebbles belong to the locality, and are 

 clearly traceable to the Greensand and to the Reading Beds. There 

 are no travelled stones from the far north and east, and, if they 

 were brought by ice, it must have been local ice ; further, there 

 is no adequate gathering-ground for a glacier in this district. 

 There are no angular stones, but all the pebbles are rounded and 

 much weathered, nor are there any scratches on them. Further- 

 more, a large number of the stones are upright in the beds, showing 

 that they dropped through water by gravitation. It is impossible 

 to conceive their dropping through ice in this fashion, or retaining 

 this position when ice was passing over them. Nor is there any 

 trace of a subglacial stream, but the deposit is clearly a widespread 

 mantle thrown down violently and suddenly, thus accounting for 

 its heterogeneous character. The speaker considered it a pity to 

 qualify the value of observations so interesting by the use of the 

 ambiguous term 'glacial' where its application is so clearly illegiti- 

 mate. Mr. Barrow had questioned the name of 'quartzite' as given 

 to some of the pebbles, and had suggested that the stones were 

 coloured pebbles from the sarsens. He thought that this was an 

 important suggestion, and one easy of proof. 



Mr. R. W. Pocock remarked that, when mapping the gravels of 

 Q. J. G. S. No. 297. e 



