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the beds have a general inclination of about 45° 

 to the south-east, and are much broken and 

 contorted ; they are of a dark greenish grey- 

 colour, faintly banded with dull buff, the strati- 

 fication becoming less apparent towards the 

 north-west ; and at 475 feet from the south-east 

 end of the cutting the dark green rock suddenly 

 terminates, resting on the upturned edges of an 

 older slate (e Plate VT.), dipping north-west, and 

 of a different character to the workable slates 

 of the Glyn and Dinorwic quarries. 



The line of junction, given in Fig. 2, is clearly 

 defined, the irregular outline of the slate (b) 

 being bleached along the line of contact. The 

 remainder of the cutting exposes a broken 

 synclinal of this '' bastard slate " interstratified 

 with conglomerates (c), which at the north-west 

 end graduate into the porphyry^ (/). The 

 synclinal trough of slate can be traced on the 

 opposite side of the lake and appears identical 

 with that marked 2*2 in Professor Eamsay's 

 section (Fig. 53, page 144, Geology of N. Wales.) 

 The slate marked 2^ is, however, I believe, not 

 a repetition of 2-2, but corresponds with the 

 higher bed of workable blue slates in the Glyn 

 quarries, in which case the point corresponding 

 with the unconformity on the south side of the 

 lake would be somewhere between the figures 

 2 and W in Professor Eamsay's section. The 

 details of structure are, however, not so fully 

 exposed here as on the south side. 



The dark green rock (a Fig. 2, and d Plate 

 VI.) resting unconformably on the "bastard" 

 slate (b) in the railway cutting closely resembles, 

 in physical character, the thin green bands in- 

 terstratified with the blue slates (Plate VII., 

 Figs. 1 and 2) of the Glyn quarries, and also 

 the green beds separating the blue from the 

 overlying purple slates. As some difference of 

 opinion was expressed at the late meeting of 

 the British Association regarding the character 

 of these green layers, it may be well to notice 

 one or two points in connection with their com- 

 position and mode of occurrence. 



With reference to their chemical constitu- 

 tion, the following analyses made for me at 

 the laboratory of the Museum of Practical 



^ This gradation of the stratified heds into the porphyry 

 is fully described in Professor Ramsay's work on the " Geo- 

 logy of North Wales." — G.M. 



