154 SUPPLEMENTARY INDEX TO VOL. IV. 
From what Mr. James D. C. Sowerby, has lately stated to me, I see 
reason also to think, that a small imconformable patch of these anomalous 
Strata (which I shall continue to call the Coices Rock , because there, my 
departed Friend Mr. Sowerby first noticed and enriched his Cabinet, 
with the peculiar Shells of these strata) rests upon the edges of the London 
Deep-Well Strata, in the vicinity of Charlton near Woolwich : also, since 
compiling the stratigraphical Index to your third Volume, I have perceived, 
that the patch dr patches of Crag-Marl in Essex, Suffolk and Norfolk, by 
lying upon the edges of the London Clay, and of its deep-well Strata, 
shews, that the Crag' must be referred to comparatively modern, uncon - 
formahle strata; but whether of the same, or a more antient or more 
recent era, than those of Paris, and the Isle of Wight &c. above men- 
tioned, I pretend not to say, but for the present shall continue to dis- 
tinguish them, and place the Crag the lowest. 
I have been much pleased to see Messrs. Conybeare and Phillips* 
introducing a set of Terms, for denominating the Orders or greater 
Divisions of the British Strata, five in number, which, if generally 
adopted, would free us from the use of those mischievously theoretic 
terms and distinctions, Primary, Transition, Fldtz, independant Coal, Fldtz- 
trap, Secondary, &c. and rid us of the many futile disputes, to which they 
have given rise, and which they seem calculated to perpetuate in Geological 
writings : the Orders of Mr. Conybeare are accordingly introduced in 
the following Index. 
As far as I could, I have availed myself of the excellent and cheap 
County Geological Maps of Mr. Smith (which are publishing by Mr. Cary, 
and sold separate) and of his Geological Table and Sections, and his other 
Publications, in ascertaining the stratigraphical places, from the Geo- 
graphical places, of the several Shells described in this Volume; and have 
little attended to, many corrections which have, as appears to me, been 
rashly offered, and continue to be repeated or varied, almost monthly, 
as to the super-position or succession, and the Names, of some of the 
English Strata, and as to their courses across, or their detached appear- 
ances, in different parts of the country. 
The number of Species of Shells named in the present Volume is 148, 
besides 4 varieties distinguished by Mr. Sowerby by (3, but which never- 
theless belong, to the same strata as their relative Shells marked a ; in 
addition to which, I have been induced to propose the separation of 12 
other varieties, partly on account of their belonging to different Strata; 
making thus 160 Species (or varieties) belonging as I believe to dis- 
tinct Strata, described in the present Volume. 
In the 46th, 52nd and 59th Volumes of the “ Philosophical Magazine,’* 
Dr. Tilioch has done me the favor to insert geographical Indexes, to the 
three former Volumes of your Min. Conch, and in a few days I intend 
to forward to him, a similar Index for the present Volume; which will 
describe the local situation and the place in the Strata, of each Shell 
figured herein. 
I beg to add 
A continuation of, and additions to the TA BLES in pages 243 of Vol. II. 
and 188 of Vol. Ill ; particularizing such species of SHELLS, as are in 
the four Volumes of this Work, and in Mr. Smith’s two unfinished Works 
on Fossil Shells , referred to more than one STRATUM ; In the Index 
■ which follows, these multislratular SHELLS are distinguished by the 
Greek Letters cc and unless otherwise mentioned below. 
Genera. Species. No. of Species, Vol. Page. 
or St rat. Var. 
Ammonites Grenoughi 2 II 71 
jugosa 2 I 2i)7 
Parkinsoni. cc, (3 & y 3 IV 182 
Dentalium cylindricum 2 I 178 
* In their “ Outlines of the Geology of England and Wales,” p. vi. &c. 
