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a great affinity,) deposits the silex, or iron, as the case may 
be, with which it was previously united, not being able to 
hold both in solution. Thus the calcareous matter of the 
shell is replaced by pyrites, or, perhaps, argillaceous earth, 
when it is lodged in shale, by flint when in the green sand, 
by carbonate of iron when in ironstone, by silica, or silicate 
of lime when in sandstone, and by carbon when in coal ; 
whilst in Limestone rocks, the carbonic acid impregnating 
water, will dissolve and subtract all the constituent elements 
of the mass, shells as well, and leave holes, passages, and 
caverns sufficiently characteristic of this formation. 
It is in this neighbourhood that Mr. Gibson, of Hebden 
Bridge, has so long laboured as a Botanist, and in search of 
fossil remains ; and not in vain, having been rewarded by the 
discovery of many rare^ and some hitherto undescrihed shells 
in the Limestone shales, or rather in what I believe Phillips 
would term the Nidderdale and Bolland, or West Craven 
Lower Shales ; the first occurring (supposing I am correct,) 
at High Greenwood, above the main Limestone, or first 
member of the Yoredale series, and the latter at Millwood, 
beneath it. 
In a letter addressed to me he thus writes — 
Sir, Hehden Bridge, Feb. Sth, 1840. 
The following list of Fossils, found in the Limestone shales in 
the vale of Todmorden, has been drawn up from specimens con- 
tained in my own cabinet, and which have, with a very few 
exceptions, been found by myself. In a railway excavation at 
Millwood, near Todmorden, the shale is of a bluish grey colour, 
and very smooth to the touch ; it contains several fossils not found 
in any other locality, particularly Goniatites proteus, which is in 
shapeless masses of dark-coloured Limestone. This stone is full of 
shells laid in every direction, and strongly cemented together, so 
that it is almost impossible to procure perfect specimens. In 
Hoolebottom Clough we meet with a few fossils of rare occur- 
rence, but our favourite localities are Crimsvvorth Dean and High- 
