58 Geological Society. 



In the bed immediately above were discovered the scale of a 

 tortoise, and the teeth of a Saurian, probably a crocodile. — 

 From the presence of two species of Serpula, the author sup- 

 poses that this series of strata might have been formed in an 

 estuary. The shells, from the occurrence of which the exist- 

 ence of marine strata in Hordwell Cliff had been before in- 

 ferred, prove to be species of Potamides, a fresh-water genus, 

 and the beds which lie above these are exclusively fresh- 

 water. 



Of the new organic remains the valves of a Cypris smaller 

 than that found in the Weald clay, but in as great profusion, 

 are characterized as the most interesting, and a small Ancylus 

 is also noted ; while the presence of gyrogonites and Ca> po- 

 lities thalictroides is quoted as completing the resemblance of 

 the Hordwell strata to those of the Paris basin. 



The author further observes, that the fresh-water strata do 

 not crop out in Beacon Cliff, as had been supposed, but are 

 continued for about a quarter of a mile or more in Barton 

 Cliff, interposed between the diluvium and white sand that 

 covers the London clay : and, scarcely hesitating to refer the 

 white siliceous sand (which rises in Beacon Cliff and is con- 

 tinued through Barton as far as the high cliff near Muddi- 

 ford) and, consequently, the analogous bed resting on the Lon- 

 don clay in Alum Bay, to the fresh-water series, concludes, 

 from the inclination of the stratum in the latter place, that the 

 fresh -water formations suffered, though in a less degree, the 

 disturbance to which the vertical strata of the Isle of Wight 

 were subjected. 



June 16. — A paper entitled, " Notes on the geological struc- 

 ture of Cader Idris ;" by Arthur Aikin, Esq. F.G.S. was read. 



The author, after describing the outline of this mountain- 

 ridge, details the relative altitude and position of the different 

 heights, the situation of the summit overlooking the crater (in 

 the bottom of which lies " the Goat's Pool") and the various 

 faces and slopes of the mountain. 



Mynydd pen y Coed, the highest hill which stands out on 

 the southern slope, is found to consist of beds of blueish-gray 

 slate very regular, and rising N.E. by N. at an angle of about 

 35°, but bending up sharply at the N.E. end, so as to increase 

 the angle to about 50°. The successive subjacent beds which 

 occupy the ground to the edge of the crater, are found to con- 

 sist of grauwacke ; compact splintery quartz with crystals of 

 pyrites, and in parts, ochry and cellular, and quartz-rock dif- 

 fering from the preceding only by being more vitreous ; which 

 last rests on a blueish-gray quartz rendered porphyritic by a 

 few crystals of felspar. These beds all rise N.E. by N. but their 



angle 



