Reviews—The Geology of Anglesey. 519 
stone has a small development of typical character, and does not 
appear ever to have had a wide distribution in the island ; after its 
accumulation occurred a final feeble renewal of the southward folding 
impulse. 
With the Carboniferous we encounter once more a widespread 
formation. Its most prominent member is the Carboniferous 
Limestone, which presents all the normal characters save for an 
unusual development of transgressive pebbly sandstones at several 
horizons. All three subdivisions of the Dibunophyllum zone can 
be recognized, and some cherts at the top of the series are referred to 
the Posidonomya zone, but nothing older can be definitely proved, 
and it is shown that the whole series disappears by gradual overlap 
in a south-westerly direction. A thin “ Millstone Grit’, with a 
peculiar kaolinite matrix, succeeds the limestone, and passes up into 
Coal Measures, which are only known from mining records, being 
entirely buried beneath the drifts and alluvium of the Malldraeth 
Marsh. Fourteen coal seams are known, mostly of small value. 
These indubitable representatives of the Carboniferous are succeeded 
unconformably by a series of red sandstones and marls, which have 
been referred to various geological horizons. The author produces 
evidence for their reference to the Upper Coal Measures, and 
correlates them with the well-known Red Measures of the Midland 
coalfields. Followimg the deposition of these beds, earth move- 
ments again took place, but the horizontal component so con- 
spicuous in the older stresses is now absent, and all the faults are of 
the “normal” type, one of them being of great magnitude. 
The Mesozoic era being unrepresented in Anglesey, though 
there is reason to believe that several of its formations were once 
deposited there, the next rocks described are the interesting Tertiary 
dykes, of which no fewer than thirty have been mapped. 
The glaciation, which next claims attention, has left traces 
everywhere in the form of drifts or ice-worn features. Numerous 
striz and trains of erratics show that the island was traversed by 
ice moving in a south-westerly direction, and the author’s evidence 
confirms the commonly accepted view that this ice formed part of 
a great ice sheet, which entirely filled the Irish Sea Basin. Hven the 
highest hills of Anglesey were deeply buried and certain overflow 
notches show that the ice sheet pressed up against the Carnarvon- 
shire mountains to the height of at least 1,700 feet. Two distinct 
boulder clays can he distinguished on the eastern coast, separated in 
places by fluvio-glacial gravels which are taken to indicate an 
important recession of the ice, though the author refuses to commit 
himself to a more precise opinion as to its magnitude. Great 
numbers of extra-insular boulders occur in the drifts, and afford an 
opportunity for some interesting speculations on the submarine 
geology of the south-eastern part of the Irish Sea. 
A final chapter on the development of the present land surface, 
which includes the consideration of the Pliocene platforms of erosion, 
