352 D. MACKINTOSH ON HIGH-LEVEL MARINE DRIFTS. 



Tryfan deposits which would appear to have escaped the notice of 

 previous observers. But before proceeding to the main subject, it 

 may be desirable to give a brief account of the discoveries made since 

 the first published account of the deposits. 



Trimmer, in the ' Proceediugs ' of the Geological Society for 1831, 

 has a short notice of the Moel-Tryfan drifts, in which he found Bucci- 

 num, Venus, Natica, and Turbo (if correctly identified) beneath 20 ft. 

 of sand and gravel. In vol. i. of the ' Journ. of the Geological Soc. 

 of Dublin' (1838), he wonders if the granite as well as the flints he 

 found on Moel Tryfan came from Ireland. [He heard of quarrymen 

 finding sea-shells on Moel Eaban, near Bethesda, where Darwin 

 afterwards could find no trace of drift likely to contain shells.] In 

 his work on Geology, published in 1841, Trimmer gives a general 

 section of the drift from Menai Strait over Moel Tryfan to Mynydd 

 Mawr. He could find granite erratics only at eight points between 

 Menai Strait and Snowdon. 



Buckland, in 1841, found rounded chalk-flints and white granite 

 in the Moel-Tryfan deposits. His paper was read before the Geo- 

 logical Society, and an abstract of it appeared in the ' Athenaeum,' in 

 1842. 



Darwin, in 1842, in the ' London, Edinburgh, and Dublin Phi- 

 losophical Magazine and Journal of Science,' gives a very sug- 

 gestive description of the Moel-Tryfan deposits. He found boulders, 

 chiefly from the neighbouring mountains, but likewise rounded flints 

 and white granite. Under the drift he saw that the surface of the 

 slate, to a depth of several feet, had been shattered and contorted in a 

 very peculiar manner. He did not find shells ; but near the summit 

 of the hill, on the east side, he saw a thickness of at least 20 ft. of 

 irregularly stratified gravel with boulders and layers of sand and 

 fine clay. He attributed the shattering and contorting of the slates 

 to icebergs grating over the surface, and lifted up and down by the 

 tides. The shattered and rounded slate rocks were similar to what 

 he had seen in Tierra del Euego. He believed that the Chalk flints 

 had been brought by floating coast-ice. 



Darbishire gave an account of the Moel-Tryfan deposits in the 

 ' Proc. of the Manchester Lit. and Phil. Soc. ' for 1851-52, and in 

 the ' Geol. Magazine,' vol. ii. He believed that a layer of yellowish- 

 brown sandy clay 1 ft. 9 in. thick had preserved the shells in the 

 underlying sand and gravel. He collected a great number of shells, 

 a list of which may be found in Mr. Shone's paper in the ' Quart. 

 Journ. Geol. Soc' for May 1878, and in Dr. Gwyn Jeffreys's paper 

 in the same Journal for Aug. 1880. 



Lyell and Symonds, in 1863, visited Moel Tryfan, and found a 

 mass of incoherent . stratified sand and gravel, 35 ft. thick, with 

 fragments of shells, and a few whole specimens. In the lower beds 

 they saw several large boulders of far- transported rocks glacially 

 polished and scratched on more sides than one. 



Eamsay and Etheridge, in 1876, examined the Moel-Tryfan de- 

 posits, and found that the boulders were chiefly local, and that the 

 sand and gravel were obliquely laminated, similar to what may be 



