114 T. M. READE OX THE DEIFT-BEDS OF THE 



At Brynker station a deep bed of this gravel (a, fig. 29)is seen to rest 

 Fig. 29. — Section at Brynker Station. 



a. Gravel. 



b. Clay. 



upon a clay (o), which is to all appearance true Till. It is quite evi- 

 dent that the esker-like mounds of gravel have been cut out of a vast 

 plateau of Drift. Moel Tryfaen, so celebrated for the marine shells first 

 found by Mr. Trimmer on its summit, is a rounded mound-like plateau, 

 forming a spur of Snowdon. It is evident that the Tryfaen gravels 

 are but an upward extension of those on the valley. Lying on the 

 slate rock of the Dorothea Quarries, Nantley valley, in 1872, 1 noticed 

 the following section (fig. 30) — purple slaty drift (2) lying on the 

 slate rock (1) in a thin patch, and over it laminated current-bedded 

 o-ravels overlain by a coarse gravelly drift (3), the total thickness 

 in the deepest part being about 45 feet. 



Fig. 30. — Section at Dorothea Quarries. 



1. Slate rock. 2. Purple slaty drift. 3. Coarse gravelly drift. 



Ascending from Pen-y-Orredd, you pass over the shoulder of 

 Tryfaen ; many sinkings for new quarries were being made, which 

 showed a great thickness of drift. There are no terraces on Tryfaen. 

 At the Alexandra quarry, just on the summit, is a bed of current- 

 bedded laminated sand and gravel containing large boulders. At 

 about 12 feet from the surface I took out a glaciated stone ; the rolled 

 gravel contains travelled granite and even flints. The larger stones 

 appear to be local. The Drift has been described by Lyell : it lies 

 upon the eroded edges of the slate rock ; and from it Mr. E. D. 

 Darbishire, F.Gr.S., collected the shells a list of which is given in the 

 table, Part I. of this paper. The level is roughly 1400 feet above 

 the sea. 



