38 MR. C. ,T. GILBERT ON" DEPOSITS OF HIQH-LEYEL [vol. LXXV r 



The only other large constituent is an occasional pebble of pudding- 

 stone from the Reading Beds, one of which measures 10 inches by 7. 

 Lenticular bands of stratified sand are occasionally met with. 



Taken by weight, a considerable part of the deposit, perhaps 40 

 or 50 per cent., consists of big flints, some as much as 14 inches 

 across. While a number largely retain the outlines of the original 

 form, they are all more or less waterworn, some of them greatly 

 so. Most of these flints, on fracture, are found to have lost their 

 original colouring, as is the case in the high-level gravels met 

 with south of the Thames. 



Taken by count and not by weight, the majority consist of 

 typical Reading pebbles, but the nodings caused by beach-hammer- 

 ing, which are so conspicuous a feature of the Reading pebbles,. 

 have in many cases been wholly or partly worn off by water-action. 

 As against this, some of the big flints and also the pebbles of 

 puddingstone show distinct evidences of the noding, alike on the 

 fractured faces of the contained flint-pebbles and on the cementing 

 material. This is of considerable importance as an indication of 

 the conditions under which the beds were deposited. While many 

 of the Reading pebbles retain their original colour in contrast with 

 the pebbles in the Glacial beds, quite an appreciable number are 

 bleached. On being fractured, they are usually found to have 

 wholly or partly lost the original dark colouring. 



As a general rule, the gravel becomes coarser in depth, the lower 

 sections containing a high percentage of large worn flints. This- 

 appears to suggest their deposition during the period of subsidence, 

 especially when taken in conjunction with the presence of the 

 loamy sands above. In no case are the pebbles crushed, as in the 

 Glacial beds. Their long axes usually are nearly horizontal. 



The spaces between the pebbles are completely filled with small 

 stones (sometimes packed together) and sand. When the material 

 comes to be sifted for road-metalling through a sieve, it averages 

 about two loads of gravel to one of sand and minute stones. 

 The sand is usually reddish brown, but occasionally } r ellowish 

 grey. It does not bind, and in this respect differs from the loamy 

 sands above, which are consolidated by a slight admixture of 

 clay. The small stones are mostly Reading pebbles and white 

 quartz, with a few lydite-pebbles. The quartz-pebbles have a 

 polished surface, often stained yellow or orange, and many are 

 semi-translucent. In some cases, nests consisting exclusively of 

 quartz-pebbles are found between the big stones. The number 

 cf these quartz-pebbles in the infilling material is very great. 



No. 2. Clay, with black-coated unworn flints and 

 small pebbles. — In the bottom of an excavation in the pit* 

 made in order to discover the nature of the basal bed of the gravel, 

 an exposure of the Upper Chalk was reached at 27 feet from the 

 surface. Between the Chalk and the gravel a bed of dark clay was 

 found. It is somewhat greenish in colour, about 6 inches thick, 

 and contains many unworn black-coated flints, broken pieces of 



