INTRODUCTION. XXXIX 
aqueous deposits that they had been spread out into beds by the action of the sea, and that 
their actual structure (though certainly metamorphic) was not the effect of torrefaction, or 
of heat emanating from any eruptive or igneous center. On the contrary, that the natural 
temperature at great depths, combined with great pressure long continued, was a cause quite 
sufficient to explain the phenomena of the old stratified plutonic rocks*. 
Many are the discussions I have held on points like these which are now forgotten; and 
I allude to them only in self-defence. 
I do not deny great merit, as well as originality, to the observations of Sir R. I. Mur- 
chison, and Sir H. de la Béche, on the stratification of plutonic rocks; nor have I the 
shadow of any complaint against either of them on this score. What I contend for is—that 
views, such as are here given, were only completed by myself after great and long-continued 
labour; that they are essential to a right interpretation of the successive groups of our 
older Paleozoic rocks; that they belong, (so far as regards this Island) to the very alphabet 
in which nature’s old records have been written, and without which her records cannot be 
read and comprehended; and that in this field of correct interpretation I preceded, by a 
good many years, all my fellow-labourers of the Geological Society +. 
4. The fourth dificulty, im making out the order of the physical groups in the 
Cambrian series, arises out of their extraordinary dislocations and contortions{. With these 
difficulties I grappled, -single-handed, in 1831 and 1832; and I so far overcame them in 
North Wales, that with one doubtful exception I was enabled to make out the general 
grouping and superposition in the very order in which it now stands in the above Tabular 
Views. 
While carrying on this task—the hardest that ever fell to my lot—I freely made use 
of M. Elie de Beaumont’s theory of parallelism, and turned it to good account: and what- 
ever may now be thought of the great, and controverted, extension which he has given to 
* A discussion on this subject took place before the British Association (I think) in 1832. It arose out of a statement 
that the bulb of a thermometer could not be maintained in the boiler of a steam-engine when the temperature was much 
eleyated. The glass bulb was dissolved by the chemical action of water heated under pressure. Hence I contended, during 
the discussion, that at the depth of ten or twelve thousand feet below the sea-bottom there would not only be a natural 
heat that was considerable, but probably a set of reagents at work capable of producing among the deposits great changes 
of structure and many metamorphic phenomena. No one, of course, contended that the actual protrusion of a mass of 
granite, or other igneous rock, was not also a true, and more powerful, agent in producing metamorphic structure. But this 
kind of direct metamorphic agency did not fall under discussion at the meeting. 
7 One, and so far as I know the only one, of the members of the Geological Society who has written on the general 
classification of the older Paleozoic rocks of England has fallen into complete error as to the epoch and origin of the 
stratified porphyries of the Cambrian age. This one great mistake inevitably damaged the whole of his Memoir on the Older 
Rocks of Wales; which is, consequently, in its beginning, in its middle, and its end, erroneous in nearly all its general 
views respecting the epoch and the order of the great Cambrian groups. 
{ This remark, so far as regards the contortions of the Middle Cambrian Group, does not apply to the “mountains of 
the Lake district” in the north of England. In that country, however, the dislocations are enormous. 
§ The exception alluded to was the doubtful position assigned to the dark, earthy slates which range near the Menai 
Straits. Ihad no doubt, in 1831, after I had examined them, that they belonged to an old group; but I could only give 
them a provisional, and not a positive place in my first sections. In 1846, when I again had an opportunity of examining 
them, I determined their right place, as they now stand in the Tabular view, under the name of Tremadoc slates. On still 
more direct and perfect evidence, Professor Ramsay has referred them to the same part of the general series. 
