187 
A SUPPLEMENTARY INDEX 
TO VOL. III. 
Arranging the Shells described therein , according to the 
several Strata in which they were found imbedded , from 
the newest towards the oldest in the British Series. 
THE following Letter, received from my kind friend Mr. Farey, which 
inclosed his manuscript of the Supplementary Index to my Third Volume, 
which he had kindly prepared, I beg to insert here, by way of preface 
to that Index. 
SIR, 
IF on the completion of my Stratsgraphical Index to your Second 
Volume, I had occasion to apologise to you and your Readers for delay 
in completing the same, I feel that I have now much greater Indulgence 
to claim, for the very protracted appearance of the enclosed Index to 
your Third Volume : and which indulgence I trust that yourself and they 
will grant, on being assured, that circumstances unforeseen and not 
within my controul, have prevented, at any earlier period since you 
finished printing the Volume, my giving that very careful, and I may 
say laborious attention, to the compiling of this Index, which I had 
determined to bestow upon it, and which now the same has had. 
It is to me a subject of the deepest regret, that since the period when 
I compiled the index to your Second Volume, only one more Number 
(the 4th) of u Strata Identified by Organised Fossils,’' has appeared, 
from the pen of my greatly respected and very ill-used friend Mr. 
William Smith ; and, that besides the three remaining Numbers of this 
work, the second part of his “ Stratigraphical System of Organised Fos- 
sils,” is also yet unpublished. 
For warn of my being able to consult the latter part of Mr. Smith’s 
Catalogue and Arrangement of Organised Fossils, and for want of knowing 
the localities, whence his specimens in the British Museum were obtained, 
with regard to all those parts of the British Series of Strata which lay 
below the Maidstone, I have experienced considerable difficulties, and 
have been in much doubt in several instances, whilst compiling the pre- 
sent Index ; suffice it to say, that I have spared no pains to do my best,' 
towards presenting a correct and useful arrangement of the Shells of this 
volume. 
Although I was by no means first in discovering the important truth , 
that particular and definable species or varieties of Shells or other organic 
Remains, are peculiar to, and not elsewhere found (fossil or living), hue 
in certain beds or definable portions (as to thickness) of the Strata of the 
Earth, yet I believe myself to have been the first to 'publish, and the most 
steady and consistent of any one else in maintaining this doctrine, so 
replete with interest, and so fertile in consequences deducible from it, both, 
of a theoretic and a practical kind : and my chief endeavours herein have 
been directed, not to the bringing forwards individual cases, wherein the 
doctrine appears to be supported ; that task I leave to yourself and 
others, whom many of my cotemporaries will be disposed to think more 
impartial evidences, and who are performing this task as effectually as 
I could w ish ; but to the pointing out, as I have done at some length in 
Vol. 53, p. 112, 120, & c. of Dr. Tilloch’s u Philosophical Magazine,” as 
many as possible of those instances, in which at present, Shells passing 
under the same name, appear from their localities, as probably referable to 
more than one Stratum each : with my earnest request, which I beg here 
to repeat, that observers and collectors of shells in different parts of the 
country, would direct their particular attention to the shells in this list, 
(of which an abstract is given in page 243 of your second volume, and 
some additions thereto which I now present,) and send up for your inspec- 
tion, as many individuals as possible, and well authenticated as to localities, 
for enabling you to discriminate and decide ? as. such accumulation of new 
facts might appear to warrant. 
