4*72 Geological Society . 



trim, iind flints occur, but rarely ; and it is worthy of remark that 

 though the gravel rests partly on quartz rock, fragments derived from 

 it are scarce. 



The beds of sand are sometimes very thin, at others of considerable 

 thickness, and tliough, for limited distances, there appears to be a 

 regular stratification, yet the beds cannot be traced to any extent, 

 thinning out in the same manner as on existing sea-beaches. The 

 shells which have been Found were, for the greater part, very imper- 

 fect, but Dr. Scouler has been enabled to determine, from well-defined 

 specimens, the following species : Turritella ungulina, Turbo lito- 

 reus, Nerita Utoralisy Buccinum undatum, Cardium edule, Cyprina 

 Islandka, and Pecten varians. 



On the opposite side of the Bay of Dublin, and to the south of the 

 promontory of Bray Head, is a similar accumulation extending for 

 upwards of a mile. At its northern extremity it presents a perpendi- 

 cular section about 200 feet high, but gradually declines towards the 

 south till it sinks to a level with the present shore. It consists, in the 

 upper part, of angular fragments of granite or syenite, and quartz 

 rock J in the middle, of numerous beds of shelly sand and gravel, and 

 in the lowest, of clay and marl. The central beds of gravel are chiefly 

 composed of fragments of limestone of moderate size, and imperfectly 

 rounded, but they also contain pebbles of chalcedony, flint, hard 

 rhalk, and a ferruginous conglomerate. With respect to the locali- 

 ties from which these materials were derived. Dr. Scouler says, that no 

 limestone occurs in situ nearer than the opposite side of the Dublin 

 granitic mountains j that the fragments of chalcedony, flint, and hard 

 chalk, appear to have been transported from Antrim, and the pebbles 

 of ferruginous conglomerate from Lambay Island, or Lyons Hill, 

 to the west of the Dublin chain. The whole of the recent species of 

 shells found at Howth, have been obtained at Bray Head, with the 

 addition of Dentalium entails. 



Besides these shelly deposits which occur adjacent to the existing 

 sea shores. Dr. Scouler describes others at a considerable distance 

 inland. One of the most remarkable of these, is in the valley of Glenis- 

 raaule, near the source of one of the branches of the Dodder, and 

 about seven miles from the Bay of Dublin. On each side of the 

 valley are perpendicular clifl^s formed of irregular beds of sand and 

 calcareous gravel, about 100 feet thick, and probably 200 feet above 

 the level of the sea. These beds are also above the level of any of 

 the calcareous strata of the immediate neighbourhood. Associated 

 withthelimestonefragmentsare pebbles of flintandchalcedony, as well 

 as recent shells identical with those in the beds previously described 

 at Howth and Bray Head. Dr. Scouler also mentions having found 

 a specimen of limestone perforated by Lymnoria terebrans. Similar 

 deposits are stated to exist in other valleys in the vicinity of Dublin; 

 and accumulations of gravel, agreeing in the arrangement of the beds 

 but difl^ering locally in the nature of the materials, to extend over the 

 whole of Ireland, forming low rounded hills, and filling previously 

 existing depressions. 



The only instance of remains of mammalia in this gravel, known to 



