1845.] 597 



are regularly furrowed in continuous parallel lines, not only from 

 top to bottom, but on each of the sides accessible to view. The 

 furrows must, therefore, be structural phenomena. 



Secondly, that the parallel markings on the conglomerates 

 oj)posite Capel Curig to the north are broader, deeper, and wider 

 apart than those of the schists which they overlie, agreeing appa- 

 rently with their wider and larger lines of bedding. 



Thirdly, that in these, conglomerates are contained fragments of 

 the schist, some of them about half a foot square, marked with 

 regular parallel flutings at equal distances, exactly in the same 

 manner as the rocks in situ. These marks are by no means in the 

 direction of the valley, but indiiferently in every direction accord- 

 ing to the position of the fragment in the conglomerate ; and the 

 matrix in which they are contained is entirely free from such 

 markings, while the furrows are not merely to be traced on the 

 exposed parts, but are continued within the substance of the con- 

 glomerate, the lower or buried sides being fluted in the same 

 manner as the upper portion. 



Hence it appears from the condition of these bedded fragments, 

 first, that glacial action could not have produced the flutings and 

 furrows observed upon them, since the direction of the furrows 

 is not that of the valley ; next, that such glacial action could not 

 have been the cause of the rounding of the rocks, since, in that 

 case, the fragments in question would have been carried away, 

 instead of left standing, as they are, half an inch above the surface ; 

 thirdly, that the rounding in question must have taken place after 

 the consolidation of the schists, but while the conglomerates were 

 still comparatively soft ; fourthly, that the furrows were produced 

 before the formation of the conglomerates, and were for that reason 

 independent of any glacial action, and, in all probability, struc- 

 tural ; and, lastly, that the furrowing and the rounding of these 

 rocks are entirely distinct and independent phenomena, due to 

 very different causes. 



Another example of furrowed rocks is seen on the right bank 

 of the lower Llanberis Lake, close to the quarry railway, and 

 rather more than midway from the upper end of the lake, where 

 a low oblong rock, consisting of a coarse bluish slate, passes some- 

 what abruptly into a conglomerate. This rock is rounded and 

 fluted, but the flutings cease exactly where the conglomerate 

 begins. 



The strice or markings not parallel to one another observed on 

 many rocks, and referred by some to glacial action, are likewise 

 considered by the author to be structural phenomena, since they 

 occur in situations where the passage of a glacier could hardly 

 have produced them, as in narrow recesses of rock, the edges of 

 which are angular, and on the projecting fragments of b?^ds, the 

 rest of which have been denuded. These striae are generally 

 narrow and shallow lines, seldom more than a quarter of an inch in 

 breadth but usually less, and some of the thinner ones, having the 



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