* 



I 



:,-■ 



i 



'. 



n» 







: 





it 



X. 





»!*• ' 



V 



-;• 



. 









f 







f 



VOLCANIC ASHES, ETC., MERIONETHSHIRE. 



183 



Slightly talcose. 



V 



particles included in a felspatliic base. Weathers to a dark 



blackish-brown. 



From the same beds as Nos. 5 to 9. It resembles No. 9. 

 The crystals of felspar were probably originally showered out 

 in a broken state and mixed with felspatliic dusty sediment. 



23. Talcose slaty beds. — Bright green, talcose, slaty 



beds, cleaved with blue slaty alternations, intersected by 

 veins of calcite. This specimen is filled with small brilliant 

 crystals of iron pyrites. This and similar beds pass gra- 

 dually into talcose and felspatliic ashes- Maps 75, N.E., 



and 74, N.W., S.W. 



Diffwys slate quarry, north of Ffestiniog, Merionethshire. 

 This bed, and several others with which it is associated, 

 is exceedingly thin in 

 quarries, and thins away entirely a little further west. 

 Eastwards they gradually thicken and their equivalents 

 swell out into the great masses that run from Llyn Conwy 

 to the Arenigs. 



24. — Talcose and siliceous felspathic ash. — Be- 

 tween Tan-y Grisiau and Cwm Orthin, Ffestiniog, Meri- 



,p 75, N.E. See 24, section 4. Brownish- 



the neighbourhood of 



the slate 



onethshire. M 



grey rock, mottled with black, showing a coarse slaty struc- 

 ture ; bleached and partly decomposed on the outer surface. 

 These rocks sometimes pass into well-marked felspathic 

 ashes, and sometimes into fossilliferous sandstones, equiva- 

 lent to the base of the Llandeilo beds. In places they also 

 assume the appearance of rocks termed Variolite. 



24a. 



d fused in afi 



It has the general appearance of obsidian, but is vesicular 

 and spherulitic See Nos. 138, Wall-Case 1, and also 



Wall-Case 2, where the same general structure 



is 



shown in obsidian, from Ascension. 



25. — Felspathic and talcose beds. — South-east of 



Cwm Orthin Lake, 



» 



Merionethshire. Map 75, 



N.E. Very compact bands of grey, dark green, and black 



felsp 



soft, and coated 



Uppee 

 Galleky. 



Wall-case 4. 



