part 1] SANDS AND GRATELS AT LITTLE HEATH. 41 



(7) The occasional big stones thrown to the top and resting on the 



smaller pebbles at the apex of the beaches at the junction with the 

 loamy sands, suggestive of tidal force. 



(8) The construction of the loamy sands in layers, with a period of 



exposure between each layer, as proved by the ripple-marks, 

 sun-cracks, and rain-pittings, again suggestive of tidal action. 



It seems probable that the beds were deposited in a comparatively 

 •shallow sea : because, in the deeper waters where the full force of 

 storms can be developed, high storm-beaches will be formed, in 

 which the pebbles are thrown beyond the reach of subsequent tidal 

 action, as at Dungeness, where (as before stated) the storm-beaches 

 have no infilling of sand and small pebbles. 



Recent researches appear to indicate that the quartz- and lydite- 

 pebbles in this district have been derived from the Lower Green- 

 sand (which crops out north and north-west of the Chiltern Hills), 

 after the final breach of the Chiltern scarp, in the gaps of which 

 the quartz-pebbles are found in great abundance. If this be 

 -correct, it would indicate not only that the materials of which the 

 gravel-beds are composed — or, at any rate, a portion of them — came 

 from the north, but also that the vast quantities of the quartz- 

 pebbles which are found everywhere in the upper plateau-gravels 

 nearest to Little Heath are derived from the same source. This 

 is a point of some importance, and one that hitherto has not met 

 with general acceptance. 



The Extent oe the Beds. 



It may be stated in passing that these beds were mentioned in 

 Prestwich's paper, 'On the Relation of the Westleton Beds... to 

 those of Norfolk ' (Q. J. G. S. vol. xlvi, 1890, p. 139), as follows :— 



' There is another Tertiary outlier at Little Heath and Potten [Potten End] 

 extending to Berkhampstead Common, or rather, it is a mass of Tertiary 

 strata preserved in a depression in the Chalk [sic], of great extent. There 

 is some appearance of Westleton Shingle, but too indistinct for description.' 



There is no doubt that he must have referred to the gravels 

 above described, as there are no other deposits in the locality to 

 which his description could apply. It is obvious that Prestwich 

 •did not realize the significance and importance of these gravel- 

 deposits, and, so far as can be gathered, the same applies to any 

 other authorities who may have visited the district. Prestwich is 

 quite wrong in saying that they are 'preserved in a depression in 

 the Chalk ' as, although it is a fact that they are found in innumer- 

 able solution-hollows in the Chalk, which are often on a considerable 

 scale, they also cap the Chalk plateau, lying quite horizontal and 

 undisturbed. The whole of Little Heath Common is dotted with 

 old pits, from which gravel has been removed for road-metalling, 

 although, owing to the abundance of unrolled and well- weathered 

 flints on the hillsides, the pits have for man}^ years ceased working, 

 and have become overgrown with vegetation. 



While it is difficult to set an exact limit to the extent of the 

 teds, surface-indications point to their extension in a more or less 



