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ferent flints, I have reason to believe that the cup-like form is the 
most frequent which a longitudinal fracture of these bodies offers to our 
view. 
That this, however, was not the only form with which these bodies 
were endued, I obtained a very pleasing proof, immediately on my 
return to town from the excursion, in which these fossils had so much 
engaged my attention. The late Mr. Jacob Forster, on leaving this 
country for Russia and Siberia, nearly about twenty years since, had 
carefully packed up his private collection of minerals and fossils, not to 
be opened until his return or death. The latter circumstance having- 
taken place, I availed myself of the opportunity offered me by Mrs. 
Forster, of purchasing some of the more interesting specimens which 
that collection contained. Among these was that extraordinarily illus- 
trative specimen which is represented, Plate XI. Fig. 8. 
The most ample proof is afforded by this specimen, of the kind of 
bodies to which this immense number of flints, spread over such a vast 
tract, owe some of their peculiar appearances. Here the alcyonium, of 
a similar species with those which are represented, Plate IX. Fig. 4 and 
8, with its surrounding cortical part, is seen, permeated with silicious 
earth, and inclosed in a mass of grey flint. On immersing the specimen 
in water for a small space of time, the flint, which is hydrophanous in a 
considerable degree, acquires transparency, and shews the alcyonium 
itself of a bright red colour, and penetrated by white fibres or tubules ; 
whilst the whole of the surrounding flint is, by the same means, disco- 
vered to be very closely filled with a white substance, which is apparently 
similar to the cartilaginous or cortical part, which immediately invests 
the alcyonium itself. 
J. however here experienced some difficulty, since the fossil alcyonium, 
which I had thus fortunately discovered, did not bear the cup-like 
form, which appears to be so very prevalent in the flints which 
had engaged our attention. This difficulty, however, disappeared, on 
considering, that the cavity, in the superior part of the ficoid fossil 
