﻿360 THE REV. J. F. BLAKE ON THE [May 1905, 



We note that * where its outcrop descends to below 900 feet in 

 crossing the deep intervening glen between Snaefell and Beinn-y- 

 Phott,' 1 it is contracted to a less breadth than that which it 

 occupies at a greater height. On descending the slope into this glen 

 from the east, near the inn where the tram-line crosses the road at 

 a height of 1341 feet, we meet with numerous exposures of ' striped 

 slates with gritty alternations,' 2 which at the base cross the stream 

 with a steady dip north-westerly in direction, and are followed 

 in the same direction by the (practically) dipless Barrule Slate 

 till the lead-mine is reached, near which the section ceases. This 

 section gives the first indication that, if the beds be not over- 

 turned, of which there is not the slightest sign, we see here the 

 lower, eastern, border of the Barrule Slates, and that they are 

 followed below by ' striped slates.' 



(2) The Snaefell Laminated Slates. 



This subdivision of the strata is included in the Geological Survey- 

 Memoir among the ' Strata of the Unseparated Tracts ' (p. 54), 

 apparently on account of their similarity to some portions of slates 

 found at other horizons, a point which does not here concern us ; 

 but Mr. Lamplugh more particularly speaks of them as ' altered 

 slate of Snaefell/ as well as ' striped slates.' As ' altered ' has 

 reference to a later effect, and ' striped ' is indefinite, it is proposed 

 to speak of them here by their main character as ' laminated,' 

 that is, divided into thin flat bands of different petrographical 

 character. 



This group is characteristically described by Mr. Lamplugh as a 



' belt of banded slates with gritty intercalations, which form the passage-beds 

 between the Barrule Slates on the west and the Agneash Grits on the east ' 

 (op. cit. p. 527) ; 



while in a neighbouring mine, situated on or near a fault, the 

 'deeper northward workings appear to enter the Barrule Slates' (op. 

 cit. p. 527). Small exposures of the same rock called ' striped and 

 puckered slate ' are seen all along that part of the mountain-road 

 that has passed to the east side of Snaefell. This, therefore, is the 

 next member in the downward succession. It is defined by an 

 alternation, not merely of colour, but of substance also. By the 

 reduction of the proportion of the gritty bands, it merges insensibly 

 into Barrule Slate; by the reduction of the slaty partings, it 

 becomes altogether a laminated grit, in which the dark, soft lines 

 are very narrow and often approximate, and the rock passes into 

 the true Agneash Grit. 



(3) The Agnea&h Grit. 



The rock which underlies the Snaefell Laminated Slate is a fine- 

 grained subcrystalline quartzite, or hardened grit, arranged in groups 



1 Mem. Geol. Surv. ' Geology of the Isle of Man ' 1903, p. 51. 



2 Ibid. p. 139. 



