THE GEOLOGY OF PUFFIN ISLAND. 79 
brachiopods, corals, polyzoa and molluscs. In places beds 
of chert and sandstone are intercalated, which, though 
unimportant in the south of England, when traced north- 
wards become more prominent, so that the shale partings 
of Astbury are the representatives of the 1686 feet of 
sandstone and shale interstratified with the 470 feet of 
limestone of Alston Moor. 
Puffin Island is a fragment of a wide expanse of this 
limestone, removed by denuding agencies, which have 
considerately left this boss severed from the mainland, 
and thus provided the L.M.B.C. with so comfortable a 
station. The limestone of which it formed a part now 
stretches in a narrow band across Anglesey from Mall- 
draeth Marsh to Red Wharf Bay, its course being marked 
by a series of villages with terrible Welsh names. Another 
tract ran up the Menai Straits; eastward it must have 
extended to the Great Ormes Head, and thus have been 
linked to the wide extent of limestone which passes up 
both sides of the vale of Clwyd to the large tracts in 
Flintshire and Denbighshire. 
The limestone in the island is a massive grey rock, 
richly fossiliferous and divided by joint planes into large 
blocks. It dips as a rule to the N.W.; several dips are 
marked on the accompanying sketch map of the island. 
The best sections are those on the north side, below the 
house, and in the cliff face at the S.W. end; the former 
shows beds of limestone with thin interstratified bands of 
shale from half to one inch in thickness, both dipping to 
the north. The latter is, however, the more instructive, 
and presents the following section taken in descending 
order :— 
Massive jointed limestone, from top of cliff. 
Shaly marl with layers of fibrous calcite 4-inch 
thick and stained with pyrolusite............ 3 inch. 
6 
