332 



sides, for a considerable distance, afford indications of having received 

 their last form from the bursting of a lake higher up in the valley of 

 the Ogwen. 



Shells, and fragments of shells, like those on the shores of the ad- 

 jacent sea, are reported by the workmen to have been found in the 

 sand and gravel at an elevated spot near Moel Taban, on the right 

 bank of the Ogwen, nearly opposite the quarries of Penrhyn. Mr. 

 Trimmer did not see them here; but on the summit of Moel Tryfane, 

 on the south of Caernarvon, towards Bethgellert, in a sinking made 

 through sand and gravel, in search of slate, at about 20ft below the 

 surface, he found marine shells in a bed of sand ; they were for the 

 most part broken, resembling the broken shells on the adjacent beach; 

 when dry, they adhere to the tongue : the fragments are too indistinct 

 to identify species; the genera Buccinum, Venus, Natica and Turbo 

 occur among them. Mr. Trimmer found similar broken shells also 

 in the diluvium of the low cliff near Beaumaris. 



Beneath the diluvial deposits of this district, when the surface of 

 the slate-rock is newly laid bare, it is found to be covered with 

 scratches, furrows and dressings, like those observed by Sir James 

 Hall on the summit of the Costorphine and other hills near Edin- 

 burgh. These furrows and dressings were noticed several years ago 

 by Mr. Underwood : they are referred to the action of the diluvial 

 currents which overspread the country with gravel: some of the 

 larger blocks amid the gravel have also deep scratches upon their 

 surface. 



Where the diluvium is argillaceous, the surface of the subjacent 

 slate has been so protected by it, as to remain sound and fit for use 

 as roofing slate up to its line of contact with the incumbent clay ; 

 but where the diluvium is of sand or gravel, admitting ready access 

 of water through it to the subjacent slate rock, the slate is often in 

 a shattered state, and bent and decomposed to the depth of many feet 

 below the line of contact. 



At the close of this Meeting, which terminated the Session, the 

 Society adjourned till Wednesday the 2nd of November. 



