20 INTRODUCTION. 
still, after a labour of seven years, I found that much remained to be done, in showing 
to what extent the classification ought to be applied to other parts of the British Isles, and 
also to foreign countries. After surveys of parts of the Continent, and particularly by 
a first examination of the rocks of this age m Russia (1841), I could not but perceive 
that formations in all respects equivalent to those I had described in my limited Silurian 
region had a vastly wide Continental range. I was also led to suspect that large moun- 
tainous tracts in North and South Wales, to which Professor Sedgwick applied the term of 
“Cambrian,” and which, like himself, I at first thought rose up from beneath, and were 
older than my typical deposits, were, in fact, nothing more than extensive undulations of 
the typical Silurian strata in a more crystalline condition. Even in 1841, that good 
geologist, the late Dr. Fitton, then President of the Geological Society, in reviewing the 
‘ Silurian System’ and its published fossils, declared that the division of the “ Cambrian ” 
from the Silurian Rocks, as regarded their imbedded fossils, was “‘ merely conventional, 
and matter of temporary convenience.’ Now, at that time no “ Cambrian ”’ fossils had 
been described ; but, when they were scrutinised by paleontologists, they were found to 
be nearly altogether well-known Silurian published types. Thus, of necessity, the 
fossiliferous part of the undescribed “Cambrian” fell paleontologically into the then 
established Silurian system. Subsequently, indeed, stratigraphical evidences were pro- 
duced, showing that the slaty rocks of Bala and Snowdon (which had been called “Cambrian” 
before their fossils were known) were not older, as had been supposed, than the Caradoc 
Lower Silurian formation, but were simply repetitions of the same strata with an altered 
lithological aspect, and thus the question was completely disposed of. 
In subsequent years, the accurate surveys of Sir Henry Delabeche, Professor 
Ramsay, and other Government Geologists, demonstrated, that there existed i Wales no 
other representative of the Cambrian Rocks than the equivalent of the Longmynd 
Mountain in Salop, which I had shown to underlie the Silurian Stiper Stones ; and hence, 
-as proved by fossils, as well as by order of superposition, the Cambrian system of Britain 
became much reduced in dimensions. 
Having already, in 1842, satisfied myself of the truth of this inference, by an exami- 
nation of North Wales, in company with my Russian associate, Count A. von Keyserling, 
I lost no time in announcing this view to my countrymen,” and it was adopted by von 
Buch and Humboldt, in Germany; by de Verneuil, in France ; and, indeed, generally at 
home and on the continent of Europe. 
The same extended application of my Silurian classification had been already made 
by the geologists of the United States, and particularly by Mr. James Hall, who 
synchronized all the ancient American deposits from the Potsdam Sandstone at the base 
to the lowest limit of true Devonian Rocks as belonging to the Silurian system. Sir 
' «Edinburgh Review,’ April, 1841. 
2 See my Anniversary Address to the Geological Society in 1842, ‘Proceedings Geol. Society,’ 
vol. iii, p. 640. 
