Writers on Fossil Shells. 113 
the many of our countrymen who wrote on Geology in this pe- 
riod, should have been so little aware, of the important aids which 
a correct knowledge of Fossil Shells would afford, towards real 
and untheoretical investigations of the internal structure of our 
Country, and regarding the early history of its Strata. 
Mr. William Martin, in 1794, began the publication of his 
** Petrificata Derbiensia,” and completed the first volume thereof 
in 1809, (having previously in the same year, published his “*Out- 
lines of the Knowledge of Extraneous Fossils,”) yet Mr. M. not- 
withstanding his industrious search through so many years, for 
perfect specimens and new species of Fossil Shells, in one of the 
most distinctly and regularly stratified Districts of England, free 
from Alluvia, and particularly rich in organic Remains, had but 
in a very slight and imperfect degree perceived, the order and re- 
gularity, with which the different species of Shells are almost 
invariably arranged, in the different beds of the Rocks he had exa- 
mined, such as Mr. Smith was fortunate enough to perceive, else- 
where, almost from the outset of his investigations. 
The works of Mr. Martiu which are mentioned above, and his 
Letter in your 39th Volume, bear ample testimony to the justness 
of the above remark, which I was particularly enabled to make, 
on the occasion of paying Mr. Martin a visit at Macclesfield, in 
April 1809, and on showing and explaining to him my Map of 
the Strata of Derbyshire, and mentioning to him the discoveries 
which had been made and communicated to me and many others 
by Mr. Smith, relative to the invariableness of the stratigraphical 
situations of Fossil Shells, and the important uses which Mr. S. 
had been able to derive from them, in commencing and carrying 
on his novel and extensive investigations of the Strata and sub- 
ficial structure of England and Wales. 
Mr. James Parkinson’s extensive research into the writings 
of the greater part of the previous authors on Extraneous 
Fossils, in our own Country and on the Continent, and his in- 
dustry and judgement in the formation and description of a large 
Collection of Specimens of such Fossils, are fully shown, in the 
three volumes entitled “* Organic Remains,” which he published 
in 1804, 1808, and 181]; which work fully evinces, until ap- 
proaching the conclusion of its third volume, the truth of the 
foregoing remarks, as tothe slight and imperfect knowledge which 
existed of the Fossil Shells, in relation to, and as the means of 
identifying particular Strata, until the discoveries, and the prac- 
tical applications of the same to the general surface of England, 
began to be made more generally known, by the communications 
of Mr. Smith and myself: and in consequence of which, Mr. 
Parkinson was led to review, to question, and at length to abandon 
many positions and opinions which had been formedand advanced, 
Vol. 53, No, 250. Feb. 1819. H in 
