298 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. 



slaty grits of Bala. These are the oldest beds in Glyder-fawr; but 

 the centre of Snowdon consists of older rocks, which are considered 

 by the author to belong partly to the Cambrian system. 



Section 4. The Menai to Y Trypan, the axis of Glyder-fawr. 

 (Scale 3 miles = l inch.) 

 N.W. A « 



3 



9. New red sandstone. 

 8. Carboniferous series. 

 7- Old red sandstone. 

 6. Ludlow shale. 



3. Lower Silxirian. Upper division. 

 2. Pitto. Lower division. 



T. Greenstone. 

 This section is the continuation westward of No. 2. 



Western side of the Snowdon Chain (Section 4). — On the line of 

 the Holyhead road the hard slaty grits continue from the central 

 greenstone axis of Glyder-fawr about three miles. At Cwm Perfedd 

 they are overlaid by a series of softer beds, consisting of schists and 

 slate, with occasional alternations of hornstone. These belong to the 

 upper division of the Lower Silurian formation. 



Between these beds and the Penhryn slate the section is interrupted 

 by the elevation of the metamorphic rocks of Bronllwyd, which con- 

 sist of semi-crystalline grits, becoming, in the lower beds, more and 

 more crystalline, until they can hardly be distinguished from green- 

 stone. This grit alternates with thin beds of schist, and the whole 

 mass preserves its bedding and cleavage unaltered. It dips south- 

 east 45° ; the cleavage dips north-west 80°. 



These rocks are overlaid unconformably by the purple slate of the 

 Penhryn quarry. These slates are of so much importance, that the 

 author describes them under a separate head. 



Section 5. From near the Menai to the east flank of Snowdon through Llanberris Pass. 



(Scale 3 miles = 1 inch.) 

 N.W. . 45 S.E. 



o- 



O 



1 





a S 



1 



^■S 



■^ 



O 



Q 



Gravel. 



3 2 1 



3. Lower Silurian. Upper division. 

 2. Ditto. Lower division. 



). Cambrian. 

 s. Slate. 

 T. Greenstone. 

 This section is a continuation westward of No. 3. 



