324 PEOF. T. G. BONNET AND EEV. E. HILL ON THE [Aug. 1899 , 



Suppose, afte r this, the deposit of Drift to hegin (in what way we 

 do not now e nquire, merely assuming the covering of frozen snow or 

 ice to remain undisturbed); upon this covering is laid, first a clay, 

 next a stratified sand, then another clay/ This completed, suppose 

 the clima te to become gradually milder. Any bare snow will be 

 melted ; it wiJl be followed, but more closely, by that far larger 

 quantity buried beneath the Drift,^ and the Drift itself, if frozen, 

 will be probably the last to yield. The latter, as the snow melted, 

 would gradually settle down. Where the ground beneath was flat, 

 it would be more or less horizontal ; M'here it was above a buried 

 hill-slope, it would finally come to rest at the same angle. 



But, where the snow has masked glens or craglcts,^ the beds of 

 the Drift might be gradually twisted, as it descended, from a nearly 

 horizontal position to one almost vertical, and its base, as that 

 became softened, would mould itself on the new surface. If 

 snow or frozen water had filled up the fissures, the Drift would 

 gradually make its way into these as sand works down an ordinary 

 pipe, though, as a rule, more rapidly. 



It might be suggested that these fissures and the inequalities in 

 the surface of the Chalk were formed by subterranean denudation, 

 as is so common in England. This is a very natural explanation, 

 and it may have sometimes happened, but we think not often — at 

 any rate as the dominant factor — because flint (especially unworn) is 

 so scarce at the junction of the Chalk and the Drift. The latter 

 sometimes has been affected by movements analogous to faults, but 

 not the Chalk, and what has happened has only been slight local 

 disturbance, not faulting in the ordinary sense of the term. 



This hypothesis obviously is not recommended by its sim]>licity. 

 Nevertheless, in our opinion, it agrees with all the facts which we 

 observed, and we cannot say that of the others. They at any rate 

 appear to be untenable, whether the one now proposed be 

 correct or not. We may be asked to state the cii'cumstances under 

 which the Drift was deposited, but, as we have intimated, this 

 question is quite separate from that which has been discussed in 

 the foregoing pages; hence we have deliberatel}^ refrained from 

 entering upon a topic still more highly controversial. 



Discussion. 



Mr. Lamplugh said that he feared that it would be difficult to 

 deal adequately with this interesting paper, if the Authoi's wished 



'■ In some places the series may be less complete. 



- How long frozen snow can be preserved is indicated by the well-known case 

 of ice under lava described by Lyell (' Principles,' lltb ed. 1872, vol. ii, p. 38). 

 For this point and the slow tliawing of the Drift, we may cite the existence 

 at Ihe present day of permanently-frozen ground beneath the subsoil in the 

 Arctic regions. 



^ The Chalk in both islands, as may be seen from exposed surfaces, has a 

 rather unusual tendency to be furrowed and grooved : channels more or less 

 semicircular in section, sometimes deeper than broad, forming on the face of 

 the cliifs and especially on their upper part. 



