Maw — Cambrian Rocks of Llanheris, 



123 



Geology indicate that it is very different to that of the blue 



slates : — 



Analysis of the Dark Green Layers (the darkest portion reprbsented 



IN Plate VII.) interstratified with the Blue Slates, Glyn Qua,rries, 



Llanberis. 



Silica 66-45 Potash 



Soda 



Carbonic Acid .. 

 Combined Water 



Titanic Acid , 0-63 



Alumina , ... 13-38 



Protoxide of Iron 1-71 



Peroxide of Iron 1*41 



Protosesquioxide of Manganese 0*91 



Lime 2-86 



Magnesia 6-28 



With traces of Phosphoric and Sulphuric Acid. 



0-05 

 0-90 

 1-30 

 3-90 



Hygroscopic Water 0-13 



99-91 



--*' . 



: , V-:^ :^^ I 





J B 



I 



is 5«t\W 



Fig. 2.— New Railway Cutting, Llanberis ; corresponding with, letters d e, on Plats VI. 



The green rock {d Plate VI., a Fig. 2) resting unconformably on 

 the " bastard " slate e contained i-,89 per cent, of magnesia and traces 

 of titanic acid. 



Analysis op Blue Slate (the middle tint in Plate VII.) interstratified 

 with the Green Layers. 



Silica 60-68 Soda 2-09 



Alumina 21-20 Titanic Acid 0-59 



Peroxide of Iron 568 Carbon 0-07 



Protoxide of Iron 0-46 Combined Water 2-70 



Protoxide of Manganese 0-16 



Lime 1-71 



Magnesia 0-88 



Potash 3-64 



With traces of Sulphuric Acid. 

 Mr. David Forbes, v^'^hq h^s obligingly made sections for me of the 

 green beds and slates and examiiit^cL'them: iui|ier the microscope, in- 

 forms me that " the slate appeared to be composed of a pretty uniform 

 mixture of grains of quartz sand with ferruginous clay, both in fine 

 division, and that the green bed vras made up of quartz fragments 

 with decomposed felspar and particles of red oxide of iron, and 

 occasionally a greenish mineral in small quantity, probably chlorite." 

 It is evident from the analysis, that the slate and interstratified 



Hygroscopic Water ............ 0-18 



100-04 



