INTRODUCTION. ly 
of the missing chapters in nature’s older Paleozoic records. There was in the frontier 
chain of Scotland even a greater chasm than I had found above the Kendal group. 
In 1831 I, for the first time, entered Wales, not without a hope of solving the old 
Palxozoic riddle; but I was again met, in Denbighshire, by a broken succession of deposits— 
almost identical with that which interrupted the section (of Westmoreland) between the 
Kendal group and the old red conglomerates. I therefore abandoned the descending 
order; and for two summers (as above stated) worked upwards from a base line near the 
Menai Straits, and established the Cambrian Series of the Tabular View; and I have now, 
I believe, put it in its true relation to the overlying Silurian Series. 
During the same summer (1831) my friend and fellow-labourer was led to that 
beautiful Silurian country which his works have made classical in the history of British 
Paleozoic Geology. He found at length—what I had sought for in vain during by-gone years 
—an apparently complete succession, which linked without a break the highest fossiliferous 
greywacké to the Old Red sandstone, and the Carboniferous limestone. I have dwelt on 
these facts only to do honour to the “Silurian System.” It not merely gave us a beautiful 
descending succession of physical groups, along with a corresponding series of characteristic 
fossils; but it rescued Paleozoic Geology (which is its far higher praise) from a very great 
difficulty which no previous observer had been able to overcome*. 
How were the successive Silurian groups determined? By elaborate field-work, by 
natural sections, and by ample lists of fossils. All the author's groups, from the Upper 
Ludlow Rock down to the base of the Llandeilo Flag, were defined, or professed to be 
defined, on the same unexceptionable principles: and we are all ready to sanction the affir- 
mation, “that so long as British geologists establish a classification founded on the sequence 
of strata and the imbedded contents, so long will their insular names be honoured with a 
preference by foreign geologists+.”. And I may venture to add, that these principles never 
have been, or will be, deserted with impunity. Down to the base of the Wenlock shale 
the Silurian groups are demonstrably established on the joint evidence of sections and 
fossils; and they are universally admitted to their right place in our great Paleozoic system. 
But below the Wenlock shale the evidence breaks down, or is misinterpreted. The typical 
Caradoe sandstone is not a continuous, but a broken group. It is made up, in fact, of two 
groups which are sometimes discordant in position; and which, if we use the Silurian 
language, belong to two different systems. It will not do to mask this mistake by the 
names Upper and Lower Caradoc. One group is a true Wenlock sandstone, the other is an 
integral part of that great collective group which I have correctly called Upper Cambrian. 
The typical Llandeilo flag is a good physical group; but in the Silurian System its 
geological relations, both to the beds above it and below it, are entirely mistaken. It is 
* One result was different from what I had at one time expected. There is (as above stated) an unknown chasm 
between the Kendal (or Ludlow) group, and the overlying rocks of Westmoreland and North Wales. This chasm does 
not arise so much from the remoyal of the highest Silurian groups, as from the absence of the lower groups of the Old Red 
Sandstone. 
} Anniversary Address to the Geological Society of London, by R. I. Murchison, Vol. m1. p. 649, 1842. 
