370 MR. H. B. WOOBWARB ON DISTURBANCES [Aug. I9O3, 



I am not stopping to discuss what some may still consider a 

 debatable subject, the character of the agent which formed and 

 distributed the Chalky Boulder-Clay. That this agent was land-ice, 

 in the opinion of most of those who have lived and laboured on the 

 Drifts, is supported by overwhelming evidence. 



Penning rejected the land-ice theory of the'Boulder-Clay, especially 

 because he found no signs of grinding or thrusting of the surfaces 

 beneath that Glacial deposit. 1 



The local evidence is now forthcoming ; and it is unnecessary to 

 do more than mention the similar cases of disturbed Chalk near 

 Trimingham and near Norwich, not to mention other formations 

 more or less disturbed beneath the Chalky Boulder-Clay in various 

 parts of the Midland and Eastern Counties, and the evidence of 

 dislodged and transported masses of Chalk and other strata. 



Attention, however, may be recalled to the disturbed Chalk at 

 Litcham in West Norfolk, described in 1866 by S. Y. Wood, Jun. 2 

 There he noticed that the lower flint-layer exposed in a chalk-pit 

 was bent into a gentle anticline, and the layers above were greatly 

 ruptured, and even overthrust. Wood attributed the disturbance to 

 land-glaciation. He noted also the presence of galls of brown clay 

 in the disturbed Chalk, and while observing that they had no 

 connection with pipes or pot-holes, he was unable to offer an expla- 

 nation. Similar pockets of clay occur in the disturbed Chalk of 

 lioyston, and the section in pit No. 1 (Great Chishall, p. 365) affords 

 a clue, as it indicates that fine earthy material may be carried into 

 chinks of the ruptured Chalk by rain-waters. 



The features, therefore, to which attention has been directed are 

 such as are familiar elsewhere, and may be ascribed to a common 

 cause : that of widespread glaciation. Nor need we be at a loss to 

 conceive in a general way what that glaciation was, while bearing 

 in mind that the main features of the country were sculptured in 

 pre-Glacial times. 



Inspired by the observations and deductions of American geologists 

 — of Messrs. T. C. Chamberlin, W. Upham, W. 0. Crosby, 3 and 

 R. D. Salisbury — we may regard the process of accumulation of the 

 Chalky Boulder-Clay as bereft of many difficulties ; and this without 

 disrespect to the prophets in this country. We have but to picture 

 a large area, a humid climate, and a mean annual temperature of a 

 few degrees only below freezing-point. We have no need to raise up 

 mountains of rock if we raise up accumulations of snow and ice, 

 for ultimately the pressure from the thickness of the mass would 

 initiate movement without the aid of thrusting by ice from higher 

 grounds. 



The base of this ice-sheet would be welded by means of ice to 

 the more or less weathered and rubbly surface-strata beneath ; and 

 w r hen movement took place, the frozen surface-deposits at the base, 



1 Quart. Journ. Geol. Soc. vol. xxxii (1876) p. 195. 



2 Ibid. vol. xxiii (1867) p. 86. 



3 I am especially indebted to a paper by Mr. W. O. Crosby, of wbich I 

 prepared an abridgment in the Geol. Mag. for 1897, p. 319. 



