496 PROF. T. G. BONNEY ON THE [Aug. I906, 



conditions. 1 It must be a filled-up cavity, such as are found in both 

 the Danish and the German islands, but are commoner in the former, 

 and a section across the ' foot ' of this Riigen cavity at right angles 

 to the plane of the paper might give such a one as we find in the 

 pit near Newsell's Park. Mr. Penning's diagram, 2 indeed, represents 

 Boulder-Clay occupying a hollow in, or banked up against, the upper 

 surface of the Chalk (his sketch is incomplete on the more southern 

 side). Even if the woodcut be an 'interpretation-section ' (I expect 

 that Mr. Penning drew what he saw), the Boulder-Clay must have 

 been in existence in that position. This clay, though not exactly 

 above that mentioned in the text, which is not shown in the 

 diagram, is said to be ' at the S. W. corner ' of the pit, and cannot 

 be more than a few feet away. 



We have yet to consider the difficulty presented by both localities 

 to the interpretation put forward by Mr. Woodward : — 



' Higher portions of debris-laden ice overrode lower portions that were 

 arrested by inequalities in the ground,' and ' to the thrust or long-continued 

 pressure of ice along shear-planes at higher levels against the crest of the scarp 

 we may attribute that belt of disturbance which occurs at elevations of 387 and 

 400 feet on the east and 535 feet on the west.' {Op. jam cit. p. 371.) 



Hypothesis again seems active in the earlier part of this quotation ; 

 while in regard to the latter I agree with Mr. Jukes-Browne that 

 for ice to have produced this disturbance along a line over 5 miles 

 long ' seems a large order,' venturing also to add that the contour 

 of the ground ought to afford some hold to this aggressive ice-sheet, 

 or else it would slide or crawl over the surface without more than a 

 little superficial scraping or rubbing. How, then, are these pits, 

 related to this contour ? Outside the one at Smith's End, which is 

 just within the 400-foot contour-line, the slope of the ground towards 

 the north is very gentle for about 100 yards, afterwards falling rather 

 more steeply to the 300-foot line, on the eastern and the western side: 

 its descent towards the north being still very gentle, for the village 

 of Barley stands on the slightly-shelving top of a shoulder, projecting 

 to the north between two shallow valleys of which the eastern is the 

 more strongly marked. The New sell's- Park pit is on a very gentle 

 slope, which descends in a generally-northward direction from the 

 500-foot contour-line: and, although this steepens a little after a time, 

 especially on the north-eastern side, it is always slight. Towards 

 the north-west the ground again rises, a change which would some- 

 what impede the advance of the ice-sheet. If, then, the present 

 contour of the ground bears any resemblance to that which it had 

 during the Glacial Epoch (and to assert the contrary would be 

 another appeal to hypothesis), the ice could not get such hold of the 

 ground as would enable it to scoop at Smith's End or to shear off 

 the requisite masses near JNewselFs Park. I submit, therefore, that 



1 After careful examination of the sections of Moen and Riigen, I am unable 

 to understand how any geologist accustomed to careful work in the field can 

 explain the disturbances of the Chalk and its association with the Glacial 

 deposits by the thrusting action of an ice-sheet. 



2 'The Geology of the North- West Part of Essex, &c.' Mem. Geol. Surv 

 1878, p. 8, fig. % 



