and on Boulders transported by Floating Ice. 183 



two sides, but from the difficulty of turning over the larger 

 ones, I do not know which case is most common. I saw one 

 large block on which the scores on the opposite sides were 

 all parallel ; and another irregularly conical one, four feet in 

 length, of which three-fourths of the circumference was marked 

 with parallel striae, converging towards the apex. In the 

 smaller elongated blocks, from six to twelve inches in diameter, 

 I observed that the striae were generally, if not always, paral- 

 lel to their longer axes, which shows that when subjected to 

 the abrading force, they arranged themselves in lines of least 

 resistance. Out of three large blocks which remained im- 

 bedded in a perpendicular cliff, the vertical sides of two were 

 scored in horizontal lines, and of the third in an oblique di- 

 rection. These several facts, especially the parallel striae on 

 the upper and lower surfaces, show that the boulders were not 

 scored on the spot where they are now imbedded, as seems to 

 have been the case with the boulders described by Mr Mac- 

 laren* in the till near Edinburgh. The contrast is very stri- 

 king in the state of the surface of these boulders, and those 

 which lie scattered high up on the sides of the adjoining hills 

 and of the great central valleys, or are perched on the worn 

 bosses of naked rock ; such boulders, as I particularly noticed, 

 present no signs of scores or strias, as might have been antici- 

 pated, if, as is supposed, they were transported on the surface 

 of the glaciers. In the quarries which I examined, namely, 

 below Bethesda, and at some little height on the eastern side 

 of the village, the till rested on slate-rocks, not worn into 

 bosses. I found, however, a rather smooth pap of greenstone 

 marked with a few deep scores. The till forms, at the height 

 probably of 600 feet above the sea, a little plain, sloping sea- 

 ward ; and between Bethesda and Bangor, there are other 

 gently inclined surfaces composed of till and stratified gravel. 

 Considering these facts, together with the proofs of recent ele- 

 vation of this coast, hereafter to be mentioned, I cannot doubt 

 that this till was accumulated in a sloping sheet beneath the 

 waters of the sea. In composition it resembles some of the 

 beds of till in Tierra del Fuego, which have undoubtedly had 

 this origin. I presume the scored, rounded, and striated 

 boulders were pushed, in the form of a terminal moraine, into 

 the sea, by the great glacier which descended Nant-Francon. 



Mr. Trimmer f reports, on the authority of some workmen, 



* Geology of Fife and the Lothians, p. 212. 



t Proceedings of the Geological Society, vol.i. p. 332, or Phil. Mag. S. 

 2. vol. x. p. 1 43. Mr. Trimmer was one of the earliest observers of the scores 

 and other marks on the rocks of North Wales. He has also remarked that 

 "some of the larger blocks amid the gravel have deep scratches upon their 

 surface." Mr. Trimmer himself found broken sea-shells in the diluvium at 

 Beaumaris. 



