xiv PREFACE. 
Canadian Naturalist). And it was high time that a shameful incubus should be shaken 
off from the breathing organs of the older Palzozoic rocks; and that they should express 
themselves once again in the language of truth and freedom. 
Tottering as I now am under the infirmities of old age, with faded senses and a 
failing memory, I am ill fitted for the part of a gladiator; but after Professor Sterry 
Hunt's bold and honest vindication of my work in Cambria, it would be on my part an 
act of moral cowardice, and a want of proper respect for the sanctity of evidence, not 
thus to speak out in the cause of historic truth and reason. 
Leaving all controversy for awhile, I may mention some other facts respecting the Cata- 
logue, which may find a proper notice in this Preface. I never saw the proof-sheets of the 
Catalogue or superintended its Jong progress through the press. There are consequently a 
few notices and expressions in it which do not strictly represent my views. The Sections on 
page 1, and page 3, were made and struck off without any communication with myself, and 
on Mr Salter’s authority they entirely rest. Instead of the groups Harlech and Longmynd— 
the second from the base of the Ideal Section on page 1—I should have preferred to write 
Llanberis, Bangor, and Longmynd Groups, and I should have placed the Harlech Group at 
the base of the Menevian. The second Section, page 3, has I think considerable value; not 
as a natural Section, but as a pictorial illustration of the relative position of certain im- 
portant groups of strata. The third plate, page 9, may be excellent in its way as a small 
Geological Map; but it is far too complicated for the use of a student unless it had been 
illustrated by sections. 
I may here remark generally, that I do not think the Upper and Lower Llandovery 
Rocks of the Government Survey ought to appear as one group; and I would place the 
Lower Llandovery at the top of the Cambrian groups, and the Upper Llandovery at the 
base of the true Silurian Rocks. This is the arrangement justified by the Sections in Den- 
bighshire: but there is a large extent of country, partly covered by the Upper and Lower 
Llandovery Rocks, with which I am very imperfectly acquainted, and which is, I think, even now, 
very inadequately described in the works of the Government Survey. 
The separation between Cambrian and Silurian Rocks is sometimes defined by a simple 
line, which shows at once the discordancy of the two deposits. On the contrary, 
the passage between the two systems is not unusually marked by a great confusion of 
deposits, by enormous masses of stratified conglomerate violently contorted or set up on edge, 
which are certain indications of a vast period of time. Many monuments of powerful eleva- 
tion, abrasion, and dislocation of the rock-masses also mark the long period of time occu- 
pied in the passage from the Cambrian to the Silurian formations. 
I do not profess perfectly to understand, or to criticise, the comparative schemes of clas- 
