﻿368 THE REV. J. E. BLAKE ON THE [May 1905, 



only history of the Manx Series of Slates which will satisfy the 

 various conditions is as follows : — First, the triad of Agneash Grit, 

 Snaefell, and Barrule Slates were laid down in regular order ; next, 

 part of them, with possibly something additional, was broken up, 

 and their fragments scattered over the still-forming mud, forming 

 the Schistose Breccia ; after which they settled down along sub- 

 radiate faulted blocks, each accompanied by the common breccia. 

 These blocks united form a nucleus (as, in like manner, did 

 Malvern, the Longmynd, and Charnwood), round (and partly over) 

 which the long series of Sulby or Lonan Flags accumulated, without 

 their stratification being governed by the strata buried beneath them ; 

 but they partook of the later movements which modified both older 

 and newer formations (see fig. 5, p. 367). 



This account, however, involves the conclusions as to the character 

 and origin of the Schistose Breccia, into which we are now prepared 

 to enter. 



Y. The Characters and Origin oe the Schistose Breccia. 



The rocks, to which the name of * crush-conglomerate' was first 

 applied by Mr. Lamplugh, have been subsequently recognized as 

 having a supposed origin to which the name of ' autoclastic ' had 

 been previously applied by H. L. Smyth in 1891. 1 That author 

 defines it thus : ' Schists formed in place from massive rocks by 

 crushing and squeezing, without intervening processes of disinte- 

 gration or erosion, removal and deposition.' Five years later, Prof. 

 C. R. Yan Hise, recognizing that a schist was only an advanced 

 stage of fracture, added the words * frequently broken into frag- 

 ments.' Rocks, however, of this character had been known before 

 the 'nineties, such as the schists at the entrance of Bardon-Hill 

 Quarry, near Charnwood Forest, but the rocks of the Isle of Man 

 do not exhibit those characters. 



All the rocks of either kind have abundant fragments, and most 

 of the fragments lie in a schistose matrix. But Prof. C. R. Van 

 Hise, in the 16th Annual Report of the United States Geological 

 Survey (1894-95) pt. i (quoted above), discussing the 'Origin of 

 Autoclastic Rocks ' (quoted by Mr. Lamplugh), points out, under 

 'Relations of Autoclastic Rocks to Basal Conglomerates' (pp. 680- 

 81), the criteria which distinguish between them, saying practically 

 that the fragments of an autoclastic rock must be 

 derived from the adjacent materials, whether they be 

 below or above ; and the rock itself may be traced into 

 an ordinary brecciated form. This is not a mere question 

 of nomenclature, but of the origin of the rocks themselves. If 

 two rocks are rubbed together, and fragments are produced, these 

 fragments must be recognized as belonging to the rocks that have 

 been rubbed ; that they belong to the same series is nothing — they 

 must be adjacent before they can be separated in an autoclastic 



1 Amer. Journ. Sci. ser. 3, vol. xlii, p. 331. 



