Correspondence — Mr. G. W. Lamplugh. 45 



tilling of large sections of the plateaux in different directions, and 

 also by the existence of actual faults. Besides the normal faults, 

 which are not infrequent among the Western isles, there occur 

 among the Faroe Islands instances of reversed faults, which probably 

 indicate disturbance of a more serious character. 



(11) The concluding section of the paper deals with the effects of 

 denudation on the plateaux. With possibly some minor intervals 

 of partial depression, the present Tertiary volcanic tracts of the 

 British and Faroe Isles have remained as land ever since the volcanic 

 period. Their valleys were probably begun before the close of the 

 eruptions, and these hollows have been continuously widened and 

 deepened ever since. The result is a stupendous memorial of the 

 potency of the agents of geological waste. While the Inner 

 Hebrides abound in most impressive illustrations of this denudation, 

 they are inferior in that respect to the Faroes. The long level lines 

 of basalt-sheets furnish, as it were, datum-lines from which the extent 

 of erosion can be estimated and even measured. There is certainly 

 no other area in Europe where the study of the combined influence 

 of atmospheric and marine denudation can be so admirably prose- 

 cuted, and where the imagination, kindled to enthusiasm by the 

 contemplation of such scenery, can be so constantly and imperiously 

 controlled by the accurate observation of ascertainable fact. 



2. " The British Silurian Species of Acidaspis." By Philip Lake, 

 Esq., M.A., F.G.S. 



In this paper descriptions are given of those species of Acidaspis 

 in the Silurian of Britain which have hitherto been incompletely 

 described. The British forms are compared with those from the 

 same system in Sweden and Bohemia. Five, out of nine, are 

 represented by the same or very closely allied species in Sweden ; 

 two in Bohemia. All the Swedish forms except one are represented 

 in Britain, and one in Bohemia as well as in Britain. 



c oiririe sifo zltzdzezestoie]- 



THE FORMATION OF CHALK BOULDERS. 

 Sir, — I venture to think that the difficulties of the diminishing 

 group of geologists who still reject the land-ice origin of the chief 

 part of our British drift-deposits will not be greatly lessened by 

 the two verj r interesting papers in your last' Number — that by 

 Prof. G. A. J. Cole on "The Destruction of the Chalk," and 

 by the Rev. E. Hill on " East Anglian Boulder-clay." There is this 

 common objection to both papers, as indeed to most of the arguments 

 put forward to support the marine origin of the drifts, that while it 

 is quite possible to ascribe certain observed phenomena to the action 

 of floating ice, it is quite impossible to explain thus the whole 

 group of facts presented by any district which is carefully and 

 thoroughly examined. The 'extreme glacialist,' on the other hand, 

 claims that the presence of an extensive ice-sheet, with its necessary 



