﻿Yol. 6 1.] OKDER OE SUCCESSION OE THE MANX SLATES. 369 



manner; and, since normally only two rocks can be adjacent to one 

 spot, three or more varieties of rock in one schistose breccia will 

 prove it to be of a different origin. This is more particularly the 

 case when the rocks on one side of the breccia are all of one kind, 

 and those on the other all of the same or of one different kind, and 

 the fragments in the breccia distinct from either. 



To determine whether a given breccia is of autoclastic origin or 

 not, we must examine the fragments that it contains with as close 

 a care as if it were a fossil, or a boulder in a glacial clay, and not be 

 satisfied with calling it a grit or a slate, any more than in the parallel 

 case with calling it a lamellibranch or a diorite. I have accord- 

 ingly obtained a considerable number of fragments from numerous 

 samples of schistose breccias, of which the following is a list : — 

 Hill Series west of Snaefell : middle bend of the zigzag, 

 Glen Auldyn ; top-section in Glen Auldyn ; base of the road north 

 of Skyhill ; Elfin Glen, Ramsey ; Narradale, lower bend of the 

 stream crossing the road; Albert-Tower Crags; Mountain 

 Road, Ramsey; part of Druidale stream; Sulby Crags; 

 Gob-y-Deigan Caves. 



Of these, the examples denoted *by the spaced type are the 

 most instructive ; and the best exposure of all is at Gob-y-Deigan 

 Caves, as it is easily accessible at most tides, and well spread out 

 over the foreshore and cliffs. But it is broken up, at its junction 

 with the black slates or shales, into numerous angular faulted 

 portions. Among the rocks here represented by isolated fragments, 

 the following varieties may be recognized : — 



(1) Many big pieces of hard laminated grit, like Agneash Grit, 

 with an irregular waterworn appearance. 



(2) Coarse-grained hard grit. 



(3) Light, fine-grained grit, with irregular outline ; seems to 

 have been partly weathered before inclusion. 



(4) Small specimens of hardened dirty clay-rock (compare A in 

 fig. 12 of the Geological Survey-Memoir, p. 67). 



(5) Unaltered beyond hardening, light shale, very brittle. 



(6) Small piece finely laminated, and another coarser piece, 

 closely resembling Snaefell Laminated Slate. 



I find it impossible to conceive how such a set of rocks, so distinct 

 one from the other, and so different from any that can be found 

 around them, could be assembled in proximity to one another by 

 any act of an autoclastic nature. It is the same with the other 

 schistose breccias ; the fragments that they contain are in the same 

 way distinct among themselves, and not to be matched with the 

 material which surrounds them in the solid state. In particular 

 may be noted certain other cases; for example, in Sulby Crags 

 the fragments in the Schistose Breccia are of various kinds mixed 

 indiscriminately, while the fragments in the area between the 

 Schistose Breccia and the contorted flags are all of one kind. In 

 the Druidale section there is a coarse grit with ferruginous hollows, 

 conspicuously unlike anything found elsewhere ; and similarly, 

 among the Hill Series, is found a large quantity of porous decayed 



