412 T. 0. Bosworth— Zones of the Loner Chalk. 



anil this basin lies in a hollow very near the edge of an exceedingly 

 steep slope into Ennerdale, where wind-action would he accentuated. 

 Tlie pool at present drains towards the north, over an outlet 

 blocked to some extent by scree, instead of to the south, as would 

 naturally be expected. 



The lite-history of this pool n\ay have been as folhnvs : — An old 

 tarn of tlie ordinary type, due to moraine or scree, was gradually 

 filled up bj' the growth of peat, as the present ones are now being 

 filled. By some means, possibly owing to excessive rainfall, water 

 began to accumulate on the surface, and this water under the 

 influence of the wind was gradually able to erode a small basin, 

 which is still much smaller than the original extent of the tarn. 

 This excavation may also be assisted by desiccation and removal of 

 matter as dust during dry periods ; thoroughly dry peat is a very 

 light material and easily blown away. 



That something of the sort has occurred is quite evident, since the 

 presence of wood on the surface clearly proves removal of peat ; 

 the chief difticulty is to account for the first formation of the pool of 

 water on the surface. It is possible that an increase of scree 

 material at the original outflow may have caused so great an 

 accumulation of water that the peat could not soak it all u[), and 

 some collected on the surface. 



In this case wind-action appears to be the primary cause of the 

 present existence of this pool : whether there ever was a tarn here 

 before is quite immaterial ; all that the theory requires is a sufficiently 

 level peat-bog, however formed. In any case some physical change 

 seems necessary to cause a reversal of the usual process of accumu- 

 lation of peat, but many reasons could be given for such a change, 

 such as blocking of an outlet b^' landslips or scree, or capture of 

 a larger drainage area by a feeder, and so on. 



On the whole this idea seems worthy of consideration as a possible 

 cause of the formation of lake-basins, at any rate, on a small scale; 

 it seems especially likely to occur in cols and narrow passes, where 

 the force of the wind is concentrated. 



IV. — Thk Zonks of the Lowkr Chalk. 



By T. 0. BoswoiiTH, B.A., St. John's College, Cambiidgo. 

 rpHE object of this paper is to suggest some niodification of the 

 JL present zoning of the Lower Chalk. 



I. Disadvantages of using Holaster sfbglobosi'S. 

 This fossil is at present supposed to characterise the Chalk 

 between the zones of Avtmouitcs varians and Actiuocmnax plenns 

 {=z B, plena), but its unsuitabilit}' is evident from the following 

 summary of its occurrences : — 



In Dorset and Devonshire Hohisiter gnhglohosus occurs in the zone 



of Ammonites varians and is absent from the Chalk above. 

 In Hampshire, Wiltshire, Isle of Wight, Sussex, and Kent it is 

 nearly as common in the zone of ^4. luirians as it is in the 

 beds above. Except in the Isle of Wight, it is not recorded 

 from the upper part of these beds. 



