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medallion portrait of the eminent French centenarian, 
M. Chevreul, Member of the Academy of Sciences, Paris ; 
and by Dr. Hodgkinson, a new form of lamp for use with 
the microscope, made by Smith and Beck. 
Mr. H. C. Chadwick gave a short communication on the 
minute anatomy of Gmntia compressa, and exhibited under 
the microscope several preparations in which the ciliated 
cells lining the chambers which traverse the wall of the 
sponge could be very distinctly seen. In another prepara- 
tion the well-known tri-radiate spicules of this species 
could be seen in situ, supporting the above-mentioned 
chambers. 
Under the microscopes Mr. Theodore Sington exhibited 
three groups of Rock sections : — (1) From the Slate Quarries 
at Llanberis : (2) from the Slate Quarries on Honister Crag, 
Cumberland: (3) from the Mountain Limestone, Castleton, 
Derbyshire. 
(1) On the west and north-east of the village of Llanberis 
are extensive slate quarries about two miles apart. Running 
diagonally across both quarries is a dyke of Greenstone : the 
sections showed the junction of the Slate and the Greenstone. 
The principal minerals contained in the Greenstone are 
Hornblende, Felspar, Magnetite, and Apatite: all traces of 
cleavage has been destroyed in the slate. 
(2) The second group of rock sections was from the green 
slates and porphyries at the Honister Crag Quarries, Cum- 
berland, intermediate in position between the Skiddaw 
Slates and the Coniston Limestone. The first section was 
from the slate used for roofing purposes, the second and 
third were from the beds immediately below the overlying 
Porphyry in which all trace of cleavage is lost, and the 
fourth is from the Porphyry. It consists of crystals of 
Felspar in a greenish felspathic base. 
