331 



von Kreise, Cassel, 1825. — Von Buch, Letter to Brongniart, Jour- 

 nal de Physique, Oct. 1822. — Zincken, Ostliche Hartz, Brunswick, 

 1825. — Hausmann, Uebersicht der jungeren Flotzgebilde im Flus- 

 gebiete der Weser, Gottingen, 1824. — Oeyenhausen,Von Dechen und 

 De La Roche, Geognostische Umrisse der Rheinlander; with Maps, 

 Sections, &c, Essen, 1825. Together with many memoirs in Leon- 

 hard's, Karsten's and other journals. 



June 8th.— Henry A. Aglionby, Esq. M.A. of St. John's College, 

 Cambridge, and of the Temple, London; Marmaduke Ramsay, Esq. 

 M.A. Fellow and Tutor of Jesus College, Cambridge ; Lord King, of 

 Dover Street; and the Rev. Edward Stanley, Alderley Rectory, Con- 

 gleton, — were elected Fellows of this Society. 



A letter was read, from Joshua Trimmer, Esq. to the Rev. Dr. 

 Buckland,V.P. "On the diluvial deposits of Caernarvonshire, between 

 the Snowdon chain of hills and the Menai strait, and on the discovery 

 of marine shells in diluvial sand and gravel on the summit of Moel 

 Tryfane, near Caernarvon, 1000ft above the level of the sea." 



The object of this paper is to point out evidences of extensive dilu- 

 vial action in that part of Caernarvonshire which lies at and near the 

 N.W. base of the mountains of Snowdonia. This district is traversed 

 in a direction from N.E. to S.W., and nearly parallel to the mountain 

 chain, by two remarkable beds of roofing slate, well known by the 

 name of Penrhyn Slate, dipping usually to the S.E. at a considerable 

 angle, and extending along a series of hills of moderate elevation, 

 between the Snowdonian chain and the Menai strait. Great part of 

 the surface of these hills, and of the still lower ground between them 

 and the Menai, is so covered by accumulations of drifted gravel, sand 

 and clay, that the slate is seldom accessible, without first quarrying 

 down through a thick bed of this diluvium. It occurs, not only in the 

 valleys, but on the sloping sides and summits of hills, sometimes en- 

 tirely covering the hills, at others accumulated around small project- 

 ing crags. It is spread indiscriminately, and with little reference to 

 the rivers that now intersect the country : its greatest observed thick- 

 ness is about 140ft. 



A large proportion of this gravel is composed of pebbles and blocks 

 of various sizes, derived from rocks that occur in Caernarvonshire • 

 many of these are less rolled than pebbles of another class, that are 

 mixed with them, and which have come from a greater distance, and 

 must have been drifted upwards by some violent inundation, in a 

 direction contrary to that of the rivers which descend from Snowdonia 

 into the Menai. Among these pebbles are several which can be iden- 

 tified with the granite, sienite, green-stone, serpentine and jiisper of 

 Anglesea : other granite pebbles agree with no rock in Anglesea or 

 Wales, and resemble the granite rocks of Cumberland ; some may 

 have come from Ireland or the S.W. extremity of Scotland. 



There are also chalk flints, which can have come from no nearer 

 source than the chalk of the county of Antrim. 



This diluvium occurs in great thickness in the lower region of the 

 valley of the Ogwen, usually from 60 to 100ft ; forming its bed, and 

 often occupying both sides of the valley through which it flows. These 



