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microscope in geological research was pointed out, and how a new 
field of geological inquiry had been opened out by the examina- 
tion of thin sections of rocks, by Porbes, Sorby, and others. 
While there was no doubt that flint had been formed by the in- 
filtration or deposits of soluble silicates or organisms — such as 
sponges, corals, &c. — thin sections or chippings of flint revealed 
under the microscope the presence of sponge, spicules, Porarni- 
niferse, Xanthidia, &c. That infiltration and deposition of silex 
held in solution was still going on was seen by the waters of the 
Danube, which had converted the pillars of Trajan’s Bridge into 
agate, &c. ; by the geysers of Iceland and other volcanic springs. 
Animals and plants also possessed the power of taking up silex 
and converting it into various organs, as seen in the sponge 
spicules, the Hyalonema and Euplectella, the Diatomaceae, and 
the siliceous cuticles of many plants. 
February 11 th. 
The President, Mr. Glaisyer, in the chair. The discussion on 
“ Plint ” was resumed ; after which examples of the various ways 
in which silex in flint exhibits itself in nature were shown under 
the microscope by the following gentlemen : 
Mr. Hennah exhibited sections of flint containing seed-vessels 
and sponge (Siphonia pisciformis ) , “artificial diatoms,” a gaseous 
deposit of silex, obtained by the process described by Professor 
Max Schultze, on which markings similar to those on some dia- 
toms were seen, and sections of quartz through the optic axis 
by which the coloured rings were shown. These objects were ex- 
hibited under one of R. and J. Beck’s new large microscopes, 
with concentric rotating stage and iris diaphragm, specially lent 
by Mr. J. Beck for the occasion. Considerable interest was felt 
in the iris diaphragm, as it was the invention of Mr. J. Brown, 
a member of the society. This instrument, with the stage, de- 
signed to meet a want suggested by Dr. Carpenter, has been pro- 
nounced the most complete microscope as yet published. 
Mr. R. Smith exhibited thin sections of flint and chert, con- 
taining Xanthidia pixidularia, corals, sponge spicules, and den- 
dritic oxides, commonly called “moss agates.” Mr. R. Glaisyer 
showed stellate hairs from Deutzia scabra and I). gracilis, sec- 
tions of silicified coniferous wood, disintegrated glass exhibiting 
markings similar to those on some diatoms, and Polycistina from 
Barbadoes deposit. Mr. J. Dennant exhibited silex found among 
the ashes of a wheat-stack destroyed by fire, and siliceous cuticles 
of wheat, Equisetum, Indian corn. Mr. T. Cooper exhibited recent 
and fossil sponge spicules and gemmules, and diatoms. Mr. 
Wonfor showed Poraminiferse, sponge spicules and corals in flint, 
Poraminiferse and other organisms obtained from a cavity in a 
flint nodule, and Moller’s diatom type slide, which had been 
very kindly lent for the occasion by Mr. T. Curteis, of Holborn. 
This slide was, in the estimation of all who examined it, the most 
