XCiy POSTSCRIPT TO THE INTRODUCTION. 
P.S. July 19, 1855. 
On returning to Cambridge before the expiration of the first week in July I read 
over the printed Introduction; and as soon afterwards as my engagements permitted I 
affixed an explanatory note to p. Ixxxy, containing some references I had _ previously 
omitted; and then drew up the Table of Contents, and added the Supplement—all of which 
were sent to the Press without delay. Before the proof-sheets of these additions were 
returned, I received a copy of Professor Phillips’ “Manual of Geology” (London and 
Glasgow, 1855), and naturally turned to his scheme of classification and nomenclature 
as applied to the older Paleozoic rocks. His scheme is given in the early part of his 
volume (pp. 101, 103, 105): and so far as regards the Cumbrian mountains and the 
adjacent parts of Yorkshire, the successive physical groups, from the Skiddaw Slate 
to the Tilestone inclusive, are copied, I believe verbatim (with the exception of a 
parenthetical interpolation of the words—* ‘Transition group”—written after the Coniston 
grits) from a scheme which was published by myself in 1852, and laid before the British 
Association, in a more expanded form, at their Annual Meeting of 1853. 
At the same meeting (1853) Professor Phillips exhibited a published geological map 
of Yorkshire (illustrative of his excellent physical and geological description of that 
county), in which he adopted, without reserve, my classification and nomenclature of the 
older Paleozoic rocks. In one district (Howgill Fells) he made a slight mistake, by 
extending the Cambrian colour of his map a little too far; so as to include within it 
some beds above the Coniston grits, which ought to have had a Silurian colour, and 
which I have considered as Silurian in everything I have of late years written on the 
subject. 
It appears, from the published Manual, that he has changed his views of classi- 
fication since 1853; so that all those parts of the Yorkshire map which he first coloured 
as Cambrian must now have another name, and be coloured as Silurian. I see no 
reason for such a change; involving, as it does, not merely a change of names, but of the 
principles of classification: and so far as I understand the sections of Wales and Cumberland, 
it is a change in a wrong direction. For the new sections I have examined, along with 
Professor M*Coy, since 1853, have tended to confirm my belief that there is no such 
thing in English geology as a great “ Middle Silurian” or “Transition group” which blends 
together the most characteristic Cambrian and Silurian types. On the contrary, that there 
is a good paleontological, as well as a good physical, separation between Cambria and 
Siluria. Enough, and perhaps more than enough, has been written on this question 
in the previous Introduction: as well as in the papers submitted to the British Association 
at their last two meetings, and printed in the Philosophical Magazine for October, November, 
and December, 1854. 
To the arrangement of the physical groups, given in the Manual (pp. 103 and 105) I 
can take no material objection. The successive groups, up to the Caradoc sandstone, and 
