Correspondence, 52 7 



NOTE ON THE CONTENTS OF THE POCKETS IN THE CARBON- 

 IFEEOUS LIMESTONE AT LLANDUDNO. 



To the Editor of the Geological Magazine. 



Sir, — An examination of the contents of the pockets in the Car- 

 boniferous Limestone near Llandudno has brought to light some few 

 fossils that may tend towards solving the problem of the origin of 

 these curious accumulations. A reference to Mr. Maw's paper on 

 the same subject in Vol. II., No. 4, of the Geol. Mag., will give a 

 clear description of the general character and position of the de- 

 posits. Those which I examined are three in number : one near the 

 Little Orme, at Nant y Gamer, and two on the Great Orme, close to ' 

 Wyddfyd Farm. At the former locality there are two large pockets 

 known ; one of these, the upper one, is now nearly emptied and is 

 abandoned, the other is an open pit of considerable size, reached by 

 an adit driven in the hill-side through the Boulder-clay drift and the 

 limestone rock beneath. This pit contains, immediately beneath the 

 drift and sharply contrasting with it, some ten yards of beautifully 

 white sand, mixed in places with equally white clay ; the clay is also 

 here and there variegated with red ; it forms the floor of one side of 

 the pit, and its thickness has not been ascertained. In the sand there 

 is in one place a thickish kind of vein, consisting for the greater part 

 of oxide of manganese ; it is amorphous and pulverulent ; this is said 

 to extend beneath the floor to a depth not yet known. On looking 

 over the clays and sands in this pocket I found traces of fossils, 

 chiefly in the former ; portions of Encrinites were tolerably plenti- 

 ful, apparently derived from the Carboniferous Limestone, the other 

 fossils were not so distinct, but may be parts of Producti ; they were 

 very fragile. The white clay was in places filled with pieces of 

 white chert, and some of the fossils may have come from this, as I 

 have no doubt this chert and that also at the base of the Boulder 

 clay on the shore, is derived from the Limestone, although I could 

 find none in situ in the neighbourhood. Some of the Limestone 

 forming the walls of the now abandoned pocket is very curiously 

 banded with white and red ; it is rather shaly or fissile, and is also 

 here and there slightly silicious ; it contains many crinoidal and other 

 fossil remains. How far back towards the old pocket the lower one 

 may extend is not yet known; it is not improbable that the two 

 may be connected. 



On examining the deposits of fire-clay with sand and chert at 

 Wyddfyd Farm, I found in the sand, or rather sandy clay, which 

 overlies the thick clay, very numerous pieces of chert, some of large 

 size ; these undoubtedly belong to the Carboniferous Limestone, for 

 they are crammed with casts of Encrinites, and resemble closely 

 what in Derbyshire are called " Screw-stones." The chert is whitish 

 or drab, but is often very much decomposed and yellowish, and 

 crumbles very readily into a kind of sand. Is it impossible that the 

 sands in the pockets may thus have had their origin ? The sand a 

 little beyond Wyddfyd Farm contains very many joints of Encrin- 

 ites, besides traces of other fossils. One piece of sand, I found, has 



