XViii PREFACE. 
finished the result of his labours, which I expected to appear in a well-illustrated volume 
in course of the year following. But having waited, as I thought, too long for the appear- 
ance of the “Silurian System,” I gave up my sketches, day-books, and _ field-books (I 
think in 1837) to my honoured friend Mr Lonsdale, then the Assistant-Secretary of the 
Geological Society, and out of these documents he made a series of sections upon a grand 
scale, which shewed the extent, and many of the details, of my work in North Wales. 
These sections were exhibited and explained by myself to the Geological Society at one of 
their evening meetings, and remained in their possession for many years. The last time I 
saw them they were in the hands of Mr Warburton, who had undertaken to reduce to a 
state fit for publication the papers on North Wales, which described the labours of Mr 
Salter and myself in the years 1842—3, and he had obtained Mr Lonsdale’s larger sections 
for assistance in this work. 
In order to give coherence to my scattered remarks on the older rocks of North Wales, 
I will first mention in chronological order the chief periods during which I investigated the 
structure of the Principality. My best work, I think, was done in the summers of 1831 and 
1832, in the manner above stated. In the spring and summer of 1833 my health broke 
down so much that I was incapable of taking the field till the autumnal season, when it 
was far too late for me to attempt the great and difficult task I had proposed to myself— 
namely, of commencing with the South flank of Cader Idris, and thence, by numerous long 
traverses, connecting my work in North Wales with the typical Silurian country on the banks 
of the Towey”. 
After studying the Sections which were laid by Murchison before the British Association 
in 1833, I felt convinced that there was an overlap between the Systems of Cambria and 
Siluria (as they were afterwards called), and we agreed to settle this question next year by a 
joint tour through the most typical portions of the Silurian country, which had been, during the 
preceding years, examined, mapped, and described in considerable detail. By this joint labour 
we hoped to clear up some points of difficulty, and to establish a good line of demarcation 
between our Groups of Strata. 
We commenced our work (in 1834) by various hasty traverses in the typical Silurian 
country, which stretches on both banks of the Towey. At first we had no matter of 
controversy, for I accepted at once my friend’s interpretation of his own Sections. I did 
not go to dispute, but to learn as it were the alphabet of the Silurian tongue. My 
* The autumn of that year was however not without its fruit: for accompanied and assisted by the present Astronomer 
Royal and Dr Whewell, afterwards Master of Trinity College, I made out in considerable detail the structure of Charnwood 
Forest, and determined the range of its single anticlinal axis; in following which towards the North we found that it 
brought up at a high angle of elevation two singular masses of dolomitized Carboniferous Limestone; but out of the line of 
disturbance the Limestone regained its ordinary type. 
