372 [April 3, 



Where liglit and air have acted, much of the delicacy of the 

 cutting has been obliterated ; besides which the surface is covered, 

 in pai-t, with heath and lichens. Notwithstanding these disad- 

 vantages, the most beautiful example of the power of a loaded 

 mass, when making its way in a slanting direction, is to be seen 

 on the high road, at the commencement of the new road to the 

 quarry, exactly within the gate-posts. In this place, the more 

 delicate strise are visible, with the flutings and furrows ; and these 

 are cut in such a manner as to show that the pressure was down- 

 wards, the action slow, and the motion irregular ; and in places 

 where I have removed the moss and heath, the surface has a 

 tolerable polish, readily perceived by any one who has seen the upper 

 quarry. In this sjDOt occurs an example in proof of slow action, 

 in the work of grooving the rock. Two semicircular grooves, 

 about an inch deep, and about a foot apart, proceed parallel to 

 one another for some distance, when they gradually curve round 

 and then meet, and one of the grooves proceeds onwards from the 

 centre downwards. The form of the grooves may be represented 

 by the letter Y. Here, as in other places, it is evident that the 

 cutting substance changed its position, and for a time remained 

 stationary, though still continuing its grinding action, since a cup 

 or cell has been foi-med to a greater depth than the fluting above 

 or below. 



With so perfect a type as that of Forth- Treiddyn, of what 

 Agassiz refers to glacier action, I have been enabled to trace that 

 action at various other points in Carnarvonshire between Tre- 

 madoc and Aber-glas-llyn bridge, and also on the other side of the 

 Glas-Uyn river in Merionethshire ; but the furrows and other 

 striking peculiarities are not so evident in these other localities as 

 they are at Porth-Treiddyn. 



In the space represented in the drawing, glacier action may be 

 observed, — 



1st, at the town rock, immediately above the village of Tre- 

 madoc : 



2dly, at the farm-yard : 



3dly, at Porth-Treiddyn, already noticed : 



4thly, at a point by the road side, where there occurs a perfect 

 sample of polished rock. This lies a little beyond the rock-crystal 

 quarry, where tabular crystals of titanite, called brookite (if I 

 remember rightly) were procured. 



Sthly, at a point near Brynteg. 



Beyond Brynteg, towards Aber-glas-llyn bridge, many other 

 examples of glacier action may be seen, which are those referred 

 to by Dr. Buckland. 



In the foregoing remarks, I have confined myself to an extent 

 of 6 or 7 miles ; but I know that there are other cases, which at 

 some future day I may explore ; and I will now conclude by say- 

 ing that I have attempted to describe one of the greatest curiosities 

 in the country, which will amply reward, by its inspection, aU 

 lovers of geology. 



