SCIENTIFIC SUMMARY. 
199 
separation of the small from the large grains by the action of currents. 
Some fine-grained sandstones have been mainly derived from granitic 
rocks, hut on the whole, the small particles of quartz have more commonly 
been derived from the breaking up of schistose rocks. Clays and shales 
-consist to a great extent of particles identical in all their characters with 
those derived from the decomposition of felspars and other minerals which 
undergo a similar change. As a general rule we meet with many grains of 
sand even in clays chiefly consisting of extremely minute granules, which 
nan easily be explained by the remarkable manner in which such material, 
when suspended in water, collects into small compound grains, which sub- 
side at a rate quite independent of what would be the velocity of subsidence 
of the separate particles if they were detached. 
“ The conclusions derived from a study of the characters of the separate 
grains are confirmed by the occurrence of what may be truly considered to 
be grains of granite or mica schist. We also in some cases meet with grains 
sufficiently large to show the characteristic structure of the still more com- 
plex rocks of which they are composed. Thin sections of some of the oldest 
slates in Wales are thus, as it were, a perfect museum of specimens of the 
rocks existing at a still earlier period, broken up and worn down into the 
sands which formed these very ancient slates.” 
The Corallian Rocks of England . — On the 10th of January last the Rev. 
J. E. Blake and Mr. W. H. Hudleston communicated to the Geological 
Society a most important paper on the Corallian Bocks of England, 
describing in great detail the series of deposits existing betwixt the Oxford 
and Kimmeridge Clays. Topographically the Corallian region is divided 
into five districts of very unequal size, wholly separated from each other. 
In the Weymouth district (I.) one section discloses 230 feet of beds 
between the Oxford and Kimmeridge Clays, made up in ascending order of 
grits, clays, marls, and oolites, gritty limestones very fossiliferous towards 
the top, clays and grits. Another section on the opposite side of the anti- 
clinal shows the same development of the central limestones ; but the lower 
series is considerably attenuated. There are hardly any corals ; argillaceous 
and arenaceous matter, always, however, more or less mixed with lime, pre- 
ponderates ; but there is a rich and varied fauna, which has strong affinities 
with that of some of the Coralline beds of other districts. This culminates 
in the Trigonia beds, which lie towards the top of the main limestone series ; 
above this the fauna inclines to Kimmeridgian, below to Oxfordian types. 
The remarkable character of the Supra-C oralline beds was noted, especial re- 
ference being made to the mineral constitution, fossil contents, and geological 
position of the Abbotsbury iron-ore. In the North Dorset district (II.) the 
thickness of the mass is much reduced, and its constitution greatly altered. 
Corals are still very rare, but calcareous sediment greatly preponderates, 
and is made up largely of comminuted shells, loosely aggregated pisolites, and 
rubble frequently false bedded ; the arenaceous base of the Corallian series, 
described generally under the term Lower Calcareous Grit, is almost at its 
minimum in the neighbourhood of Sturminster. The central limestones 
contain a moderate assemblage of the usual Coralline forms, but Cidaris 
florigemrna appears confined to a rubbly bed about 8 feet thick. The 
West Midland range (III.), extending from Westbury to Oxford, exhibits 
