by means of their imbedded Shells, &c. 119 
the alternations of Beds possessing very different Mineral Qualities 
(rather than by those qualities themselves) ; and above all, with- 
out the concurrence of such characteristic organic Remains, as 
great numbers of Beds contain, and a still greater number, have 
such in their vicinity, of which pracitcal Geologists and Naturalists 
may avail themselves. 
’ | am not sanguine enough to expect to see in my time carried 
into effect, all which I have been speaking of and recommending, 
as to the examination and description of the species of Organic 
Remains, which at present but doubtfully characterize their Beds, 
owing to the number of other Beds in the English Series, in which 
very nearly similar Remains are deposited; so nearly similar, 
indeed, that no writer has yet attempted the investigation and 
mention of their specific differences, in several instances: yet as 
Mr. Smith has uniformly been heard to declare, that he always 
could, with regard to Specimens of Organic Remains which he 
had examined 2m sifu, and brought together, perceive differences 
which directed him in arranging them afterwards on his Strati- 
graphical Shelves, independent of the name of the Place whence 
they were brought, which was marked on each; (he has 
spoken to this purpose in several parts of his works; and I am 
myself of the same opinion as Mr. Smith on this point) I have 
been anxious to present to your readers, and to those of Mr. Sow- 
erby and Mr. Smith, as complete a List as I am able, of all the 
Shells which at the time of compiling it, had been referred to more 
than one Stratum in the English Series, in the writings of Mr. 
Sowerby and Mr.Smith, asis mentioned p.550 (of the last volume). 
I am aware that this List, in all probability, contains errors, 
which I have not had the means of detecting, regarding the lo- 
calities of some of the Shells, and regarding the Strata from which 
others of them were obtained by Mr. Sowerby, through the me- 
dium of his Friends and Correspondents ; Mr. Sowerby as well as 
myself, will be thankful, that all such errors may be pointed out 
to Mr.S., in order that they may be corrected in the future Num- 
bers and Indexes of his work. 
I beg, in conclusion, to take this opportunity of earnestly so- 
liciting he co-operation of the Collectors of Fossil Shells through- 
out England, with my friend Mr. Sowerby, by the gift or the loan 
to him of any Shells, of which they know the precise localities, 
which appear to be of any of the Species enumerated in the List 
which follows : in order, that more extended comparisons may 
be made, and that distinct Names may be given, in the future 
numbers of Mineral Conchology, to all such Shells in this List, 
as shew real marks of distinction, however unusual or minute they 
may be, provided only, that they are unvaryingly found in the In- 
dividuals of the same Bed. I am, yours, &e. 
Howland-street, Dec. 21, 1818. Joun Farry Sen. 
Hs An 
