to the surface oxidation, and having that slight smoothing 

 of the edges, which is the result of chemical solution of a 

 minute part of the silica. They are the same in appear- 

 ance and condition as those found covering the upland, 

 and as they lie in a tumbled irregular mass, are generally 

 as clean as if they had been hand-gathered off the fields, 

 and shot out of a basket. Good sections of such gravel 

 may be obtained at Green Street Greens, Darenth, and 

 Cray, as well as elsewhere. There may be observed in 

 them, however, layers which contain an admixture of fine 

 sand and clayey gravel, evidently the result of a flush of 

 water which has flowed over the gravel. Generally these 

 layers of loam and sand are thin, but at Longfield, on the 

 South side of the valley, they may. be seen of some thick- 

 ness, as brickearth, clean stones, then brickearth, clean 

 stones again lying on chalk. (See PL vl. fig. lo.) 



As I have said, the stones are clean and only fine 

 material lies between them, shewing that something must 

 have filled the interspaces, otherwise the light loams and 

 sands washed over them would have penetrated the inter- 

 spaces and solidified the mass much more. I think it 

 extremely probable that snow or snowy chalk filled the 

 spaces into which the finer materials could not penetrate 

 at the time of flowing. 



These alternate layers of sandy loam seem to tally with 

 the intervals between the severer fits of glaciation. 



The rain washed the fine mud from the clay-with-flints 

 leaving the stones on the surface, where they accumulated 

 loose and unattached to the soil, then came a time when 

 the rain was replaced by snow, which enveloping them, 

 scraped off the stones, carried them into the valleys, and 

 thawing, left them there ; then again a period of rain which 

 washed the upland clay from the flints, which a return of 

 snow and ice trailed subsequently into the valleys. 



This repetition may be observed, but it may not have 

 been and probably was not the whole series of the above 

 mentioned occurrences, and in the period in which we are 



