48 Reports & Proceedings—Liverpool Geological Society. 
almost wholly of one ingredient only, and may be crinoidal, coralline, 
polyzoan, or foraminiferal. The problematic organism, Calcisphera, 
is found throughout the series, and sometimes occurs so abundantly 
as to form a substantial proportion of the mass of the rock. Small 
detrital quartz grains are rarely absent, and at times the quantity is 
so great as to give am arenaceous character te the beds. The insoluble 
residues consist in great part of tiny bipyramidal crystals of quartz, 
which have not been observed to have grown around worn grains. 
but in some cases growth in two stages is indicated by a perfect 
zonal structure. Hndothyre are the principal foraminifera, 
occasionally forming the principal bulk of the rock. Valvulina and 
Archeodiscus are very common, particularly in the Upper Grey beds, 
and Teatularia and Trochammuna are also frequently met with, while 
Nodosaria is always extremely rare. 
Oolitic limestones are se!dom found, and seem to be confined to the 
Lower Brown and Upper Grey beds near Denbigh and Gwaenysgor, 
in Flintshire. Dolomites also are not very widespread, and occur 
principally in the Lower Brown, where they appear to be of 
subsequent origin, being associated with mineral veins and fault 
fissures. Calcareous alge, again, although not entirely absent, seem 
to have played a negligible part in the building up of the rocks. It 
would appear, therefore, that the lagoon conditions which were so 
prevalent in South Wales and also in the North-West of England, 
were not characteristic in anything like the same degree of the North 
Wales area, although the limestones must have been deposited for 
the most part in quiet, shallow waters. Itis not improbablethatthey 
were accumulated in an island-studded sea, on an uneven floor 
(for the various beds do not seem to have any great lateral extent), 
and not far from a low-lying mainland, which ‘for the greater part 
of the period contributed very little sediment. The Middle White 
Limestones, which are much more massive and uniform in character 
than the beds above and below them, represent deeper water 
conditions. They are generally of great purity, the jpenvennialze of 
CaCO, often approaching 99. 
