488 Horace B. Woodward — The Chalky Boulder-day. 



masses and pinnacles of unweathered limestone. Some of tlie more 

 remarkable accumulations of rubble occur to the north-west of Break 

 Heart Hill, south of Dursley ; near Gravel Farm, south of Hares- 

 comb ; at Leckhampton Hill, where the rubble is banked up at angles 

 of 30° or 40° ; and west of Syreford, near Andoversford. Frequently 

 there is a considerable thickness of brown loamy clay on top of the 

 oolitic rubble — the residue of atmospheric waste, indicating some 

 lapse of time. 



This material has been described by Strickland, Hull, Lucy, 

 Witchell, Prestwich, and others. Mr. Lucy connected the distribu- 

 tion of the rubble with soil-movements, the weathered rock slipping 

 down the hill-sides during times of thaw after severe frost.^ In 

 Witchell's opinion, this Eubble Drift was " due to storm- waters or 

 surface-drainage, which brought the detritus down the hill upon 

 a frozen surface, and deposited it in those places where the frost 

 usually disappeared in spring before it left the higher ground." '^ 

 Both explanations may be to a certain extent true, and they accord 

 much better with the facts than does the explanation of Prestwich, 

 whereby this Eubble Drift would be due to the effects of wide 

 submergence.^ 



In studying the general characters of the Glacial Drift, several 

 problems of special interest come under notice. Among these are 

 the abundance and wide distribution of chalky detritus ; the distur- 

 bances produced in underlying strata ; the occurrence of the larger 

 blocks or " cakes" of local origin ; and the intercalation of the gravels 

 and sands with the Chalky Boulder-clay. If, following Crosby, we 

 believe that the earlier action over the glaciated areas was the 

 removal of the weathered soil and subsoil which was frozen to the 

 base of the at first sedentary ice, we may conclude that the major 

 disturbances in the underlying strata were then produced, together 

 with the striated pavements which are very rarely, of course, to be 

 found in these Midland areas. Although " drag " is not admitted 

 as a likely mode of transport of the ground-moraine, yet, when this 

 material was in movement at the base of the ice-sheet, and as it was 

 shifted from its original position, there may have been some dragging 

 of the substrata, leading to contortion and " terminal curvature." 



The researches of Messrs. Chamberlin, Uphara, and Crosby have 

 shown how materials from the ground-moraine become " englacial " 

 — being carried by overthrusts of ice to higher positions in its mass. 

 In fact, much detritus is thus shifted along planes of slipping, when 

 inequalities in the land cause higher portions of the ice to move 

 obliquely upwards and over lower portions. Parts of the original 

 stony base of the ice-sheet may here and there, however, have been 

 left in the hollows of the irregular land-surface until the final melting 

 of the ice. Had the icy agent overspread the Cotteswold region, 

 the Eubble Drift before-mentioned would have largely contributed 



^ Proc. Cotteswold Club, vol. v, p. 43. 



^ Proc. Cotteswold Club, yoI. vi, p. 150 ; see also H. B. W., " Jurassic Eocks of 

 Britain," vol. iv, pp. 462-3. 



2 Quart. Journ. Geol. Soc, vol. xlviii, p. 314, 



