Yol. 56.] EARTH-MOVEMENT IN THE ISLE OF MAN. 11 



3. On some Effects of Earth-movement on the Carboniferous 

 Volcanic Kocks of the Isle of Man. By G. W. Lamplugh, 

 Esq., E.G.S. (Read December 20th, 1899.) 



[Communicated by permission of the Director-General of 

 H.M. Geological Survey.] 



I. Introduction. 



In a paper brought before this Society four years ago by Prof. 

 W. W. Watts and myself, attention was drawn to some peculiar 

 effects of earth-movement on the older Palaeozoic rocks of the Isle 

 of Man. 1 These rocks, constituting the Manx Slate Series, are 

 unconformably overlain by Carboniferous strata in the south of the 

 island, and from the manner in which the Carboniferous Basement 

 Conglomerate evenly overspreads the denuded edges of the folded, 

 cleaved, and crushed slate-series, it is certain that the movements 

 which so profoundly modified the slates were of pre-Carboniferous 

 age. This evidence led me at first to suppose that the region had 

 undergone very little disturbance in later times, and further 

 evidence tending to the same conclusion seemed to be afforded by 

 the fact that the Carboniferous-Limestone outcrop in the south of 

 the island, though traversed by numerous minor dislocations and 

 undulations, nearly always presents a low dip and shows no readily 

 recognizable indication of exceptional disturbance. 2 



Before completing the mapping of the island in 1897, however, 

 I had occasion to re-examine the magnificent coast-section in the 

 Carboniferous Volcanic Series between Castletown Bay and Poolvash 

 (Poyll Yaaish) with the hope of clearing up some outstanding difficul- 

 ties in regard to the relations of the limes tone to these volcanic rocks 

 which several previous examinations had failed to elucidate, and, 

 being favoured by exceptionally low spring-tides, I then discovered 

 evidence which threw new light upon this point. Both at the 

 eastern and at the western extremities of the volcanic outcrop, 

 this evidence indicated that the strata had undergone deformation 

 of an extraordinary type subsequent to their deposition, and that 

 many of their complex structures, hitherto supposed to be essentially 

 due to the eruptive outburst, were, in fact, superinduced structures 

 due to earth-movement. Two further re-examinations of the critical 

 sections which I have made under similar circumstances during the 

 present year, on the first visit accompanied by Dr. Wheelton Hind, 

 Mr. J. A. Howe, and my colleague Mr. "Walcot Gibson, and on 

 the second by the Director-General of the Survey, have confirmed 

 me in the conclusions reached in 1897. As my official memoir 

 on the island, containing a detailed description of the sections, is 



1 ' The Crush-conglomerates of the Isle of Man ' Quart. Journ. Geol. Soc. 

 vol. li (1895) pp. 563-97. 



2 Ibid. p. 585. 



