﻿358 THE REV. J. F. BLAKE ON THE [May I905,. 



16. On the Order of Succession of the Manx Slates in their 

 Northern Half, and its Bearing on the Origin of the 

 Schistose Breccia associated therewith. By the Rev. John 

 Frederick Blake, M.A., F.G.S. (Head February 22nd, 

 1905.) 



I. Introduction. 



Among the slates of the Isle of Man some strata have been found 

 which represent, in the opinion of Mr. G. W. Lamplugh, so distinct 

 a type of phenomenon that he assigned thereto a special name — that 

 of a 'crush-conglomerate.' In the earlier announcement of this 

 result in 1895, 1 he denned the rock as ' made up of scattered frag- 

 ments set in a slaty matrix,' and considered it 'due to the breaking- 

 up under pressure of alternations of flaggy slate and thin grit-bands' 

 (op. cit. p. 565). So far as this general statement goes, we shall 

 find it included in the description of many fragmental rocks ; but 

 when we seek further information, and enquire concerning the 

 fragments whether they be angular or round, scattered or crowded, 

 uniform or various, composed of neighbouring rocks or of remote 

 ones, and of the pressure, whether it be shearing or otherwise, 

 metamorphosing or not — then our troubles begin. 



The paper in the Quarterly Journal was only a preliminary 

 account of what had been observed, and a full statement was 

 promised when the Geological Survey-Memoir on the island should 

 be published, which took place in 1903. I had early, however, 

 taken an interest in the question, owing to the inclusion by 

 Sir Archibald Geikie of some rocks in Anglesey in the same 

 category. 2 But 1 had not to wait so long as 1903, for, with 

 the greatest kindness, Mr. Lamplugh lent me some advance-proofs 

 of the principal passages involved, and thereby enabled me to spend 

 portions of four successive summers in the island, amounting in all 

 to about seven weeks of consecutive work, in examining all parts 

 likely to throw light upon the subject, with the aid of the 6-inch 

 maps as shown in the office of the Geological Survey. 



From a study of the literature thus made available, it soon 

 becomes apparent that a primary stage of the investigation consists 

 in a determination of the lie and position, and thereby of the order 

 of succession, of the Manx Slates in which these strata lie. 



II. The Order of Succession of the Manx Slates. 



The determination of the order of succession of the various 

 members of the Manx-Slate Series is a matter, on the whole, of 

 considerable difficulty : owing, in the first place, to the relative 

 paucity of exposures over wide areas, the solid rocks being much 



1 Quart. Journ. Geol. Soc. vol. li, p. 564. 



2 Geol. Mag. 1896, p. 481. 



