200 Maw— Pockets in Mountain-limestone. 
III. On some Deposits or CHERT, WHITE SAND, and WuHiTE CLAY 
IN THE NEIGHBOURHOOD OF LLANDUDNO, NortH WALES. 
By Grorcr Maw, F.LS., F.G.S., F.S.A., & V.P. of The Severn-Valley Field-club. 
[Plate VII.] 
\eeue a mile and a half to the east of Llandudno, forming the 
eastern boundary of Orme’s Bay, a range of Mountain-limestone 
runs from the Little Orme’s Head on the coast nearly to Conway, 
enclosing between it and the Great Orme’s Head, to the west, a flat 
tract of ground, which appears to consist for the most part of 
Boulder- -clay overlain by a more recent alluvium. 
A coast-section towards Colwin, to the east of the Little Orme’ s Head, 
exposes the ordinary tough blue Boulder-clay, an overlying reddish 
loamy clay and sand, and a still more recent alluvial deposit, consisting 
of tough grey clay, interstratified with seams of peat. Immediately 
adjacent to the Little Orme’s Head the Mountain-limestone is seen 
coming up under the Boulder-clay, the very base of which consists 
of a hardish breccia of chert, intermixed with fragments of Moun- 
tain-limestone and Mountain-limestone fossils: but the chert would 
appear to be of a different age from the Mountain-limestone, as I could 
detéct none of the chert-bands which occur, in some districts, in the 
formation of the neighbourhood; nor did any of the fragments of 
chert give indication that they had been broken from a limestone 
matrix. In Orme’s Bay, on the west side of the Little Orme’s Head, 
the base of the Boulder-clay is still more largely charged with 
chert-fragments; and its body, instead of being of the ordinary dark- 
blue colour, is of a rich ochreous brown. A few feet above high- 
water-mark, however, the normal colour commences ; and here and 
there, up to the top of the cliff, thin layers of white chert-fragments 
are irregularly distributed, as though at the setting-in of the Boulder- 
clay formation large quantities of chert had been denuded, and 
occasional accessions of the material had continued to take place 
during the whole of its deposition. I refer to the development of the 
Quaternary deposits of the neighbourhood, to show that the forma- 
tions about to be described preceded their deposition, and were 
being denuded at the commencement of the deposition of the 
Boulder-clay. 
The bulk of the hilly ridge at the back of the Little Orme’s 
Head is principally exposed as naked limestone crags, from 300 
to 400 feet in height; but in some places the rock is hidden up to a 
height of from 200 to 250 feet by débris and Drift, which may pro- 
bably be, in part, the remains of a once higher extension of the 
Boulder-clay, as many of the boulders composing it are striated, and 
appear to have come from a distance. 
At aspot called Nant-y-Gamer, on the western slope of the range, 
about half a mile from the sea, a mile from the Little Orme’s Head, 
and a mile and a half to the east of Llandudno, some curious cavities 
or ‘Pockets’ occur in the Mountain-limestone, the existence of 
which has been obscured by the uniform covering of débris. The 
Drift is here from 10 to 20 feet in thickness, occasionally thicker, 
and spreads with tolerable uniformity over the solid limestone and 
