PREFACE. XVil 
Karly next summer I resumed my task in Wales. Crossing the depression in which 
my sections had terminated, I pushed them forward towards the East, nearly at right angles to 
the strike of the strata; and in the progress of my work, discovered the great Merioneth-Anti- 
clinal, which I have often called the backbone of Wales. It brings out the oldest strata which 
were first seen near the coast of the Menai; and assuming it as our base, we can count off 
towards the East an enormous series of ascending strata capped by the whole Bala group; 
and from the same base-line we can count off all the groups of the three sections observed in 
the preceding year, first in ascending, and then in descending order, till we meet the same 
basic groups as we approach the shores of the Menai. 
Having thus obtained a key-note to the harmonious grouping of the strata, and having 
practically become acquainted with some of the most important physical groups, I under- 
took what proved to be the severest summer’s task of my Geological life; namely, the 
interpretation and partial delineation of the order and principal flexures of all the older 
deposits of the counties of Merioneth, Montgomery, and Denbigh. 
A brief synopsis, illustrated by sections of what I had effected in Caernarvonshire, was 
laid before the British Association, at one of their evening meetings held at Oxford in the 
year 1832. I had no doubt about the great groups or about the great flexures and faults 
by which some of them were repeated again and again in the same county. 
I never had a Geological secret in my long life. Nearly all my best work in Wales 
was done in solitude, and was therefore my own. My first groups continue unchanged 
and unmodified; with the exception of certain changes introduced by recent discoveries, such 
as the Menevian group, which now forms a group subordinate to the Lingula Flags; and I 
hesitate not to affirm that the grand and well-connected succession of deposits which I 
unfolded between the Menai and the top of the Berwyn chain is unrivalled by any other 
European Section, of the same age, hitherto described by Geologists. The Cambrian sections 
have this crowning honour; and are rivalled in their succession and physical development only 
by the magnificent series of Paleozoic rocks discovered by the Geologists of North America. 
What sense therefore has there been in excluding the Mountains of Wales from their 
proper physical importance in the Geology of our own Island by sinking them and colouring 
them as Lower Silurian? The groups of the Lower Silurian System of Sir R. I. Murchison, 
(even had their place and age not been utterly mistaken by their Author,) would not have 
deserved the prominent notice they have held in the nomenclature of English groups; for 
they generally want the essential condition of good typical groups. They de not shew any 
true relation to the groups above them and below them. 
For my own convenience I had made an agreement with the Author of the Silurian 
System, at the Edinburgh Meeting of the British Association, in 1834, to wait till he had 
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