NORTH-WEST OF ENGLAND AND NORTH WALES. 



115 



In the cuttings of the railway from Bettws up the Dolwydellan 

 valley, which I inspected in February 1876, while under construc- 

 tion, small patches of stratified gravel are here and there intersected ; 

 but, as a rule, very little drift was met with. About three quarters 

 of a mile from Bettws a cutting in the slate rock disclosed a 

 singularly smooth surface which had been protected by a cover of 

 drift ; it was not planed down, but was in undulating dimples and 

 hollows, smoothed as if ground with polishing paste. This was very 

 instructive, as where the rock was unprotected by drift on the same 

 shoulder, close by, without any transition, the rock was jagged and 

 irregular. 



On a rock near to the mouth of the tunnel, but not on the line of 

 railway, towards the summit-level of the railway, some singular 

 markings were to be seen. They appeared as if gouged out at all 

 angles ; I have never seen any thing like this before or since. 



Slate rock. 



b. Drift. 



In inspecting some excavations made for a sett quarry near the 

 Rivals mountain, I was struck with the jagged nature of the rock 

 underlying the drift {a, fig. 31), the very antithesis of that I have 

 described near Bettws. The drift b was compact and solid argilla- 

 ceous matter or Till, full of rough stones intermixed with angular 

 and subangular ones : some of the stones were erratics ; but most con- 

 sisted of the local felstone porphyry. I must bring this account of 

 the Welsh drift to a close by a description of the section disclosed by 

 the excavation of the puddle-wall of the Rhyl Reservoir* (fig. 32). 



Fig. 32. Rhyl Reservoir, Nant Uwydd ; section of puddle trench. 

 (Horizontal and vertical scales 220 feet to 1 inch.) 

 JntendiS, water 7zne 



Here we have : — 



A. Bed rock, Denbigh Shales, getting more slaty in structure 

 towards y. The floor is quite level ; but the beds dip up the valley at 

 an angle of about 12°. The sides are stepped. 



B. Fine waterworn gravel, angular and larger near the bed-rock. 



* I ain indebted to Mr. H. C. Beloe, the engineer of the works, for this in 

 formation. 



Q. J. G. S. No. 154. x 



