"The deposits on Moel Tryfaen are exposed in a slate-quarry on the northern aspect of the hill near the summit, and consist of two wedges of structureless boulder-clay, each thinning towards the top of the hill. The lower mass of clay, wherever it rests upon the rock, contains streaks and irregular patches of eccentric form, of sharp, perfectly angular fragments of slate; and the underlying rock may be seen to be crushed and broken, its cleavage-laminæ being thrust over from northwest to southeast--that is, _up-hill_. The famous 'shell-bed' is a thick series of sands and gravels interosculated with the clays on the slope of the hill, but occupying the entire section above the slate towards the top. The bedding shows unmistakable signs of the action of water, both regular stratification and false bedding being well displayed. The stones occurring in the clays are mainly if not entirely Welsh, including some from the interior of the country, and they are not infrequently of large size--two or three tons' weight--and well scratched. "The stones found in the sands and gravels include a great majority of local rocks, but besides these there have been recorded the following: Rock. Source. Highest Minimum point uplift _in situ_. in feet. Granite Eskdale, Cumberland 1,286 64 Granite Criffel, Galloway ..... ... Flint Antrim (?) 1,000 350 To these I can add: Granophyre Buttermere, Cumberland ..... ... Eurite [BU] Ailsa Craig, Frith of Clyde 1,097 253 [Footnote BU: The altitude at which this rock occurs on Ailsa Craig has not been announced, so 1 have put it as the extreme height of the island.] "The shells in the Moel Tryfaen deposit have been fully described, so far as the enumeration of species and relative frequency are concerned, but little has been said as to their absolute abundance and their condition. The shells are extremely rare, and daring a recent visit a party of five persons, in an assiduous search of about two hours, succeeded in finding _five whole shells_ and about two ounces of fragments. The opportunities for collecting are as good as could be desired. The sections exposed have an aggregate length of about a quarter of a mile, with a height varying from ten to twenty feet of the shelly portion; and besides this there are immense spoil-banks, upon whose rain-washed slopes fossil-collecting can be carried on under the most favorable conditions.