xl INTRODUCTION. 
it, I can only express myself towards him (as I have done before, many years since, when 
I was President of the Geological Society of London), in terms of gratitude for the great 
help which his works, on the theory of parallelism, have lent to me. Viewed in connexion 
with that theory, the Cambrian series becomes a vast and complicated system; which, as a 
general rule (however modified by local dislocations and subsequent contortions), has a 
north-eastern and a south-western strike; and with that prevailing strike is thrown into great 
parallel undulations, which, in many parts of the British Isles, were completed before the 
existence of a single Silurian deposit. So great has been the physical influence of these 
old north-eastern and south-western movements of elevation, that (within the limits of the 
British Isles) we can often decide upon the date of the older constituent deposits of a 
given region, by a glance of the eye over the physical map in which they are delineated, 
and where their north-eastern strike has produced its characteristic impress on the geogra- 
phical surface. Thus, for example, in the Isle of Man (in which I have never set my foot) 
I should conclude, from the outline of the map, that the slate-rocks had a north-eastern 
and south-western strike; and hence, that they were probably Cambrian, and not Silurian*. 
* The best English illustration of the parallelism of contemporaneous axes of elevation, with which I am acquainted, is 
to be found in Charnwood Forest, in the Warwickshire (or Nuneaton) coal field, and in the beautiful Silurian groups near 
Dudley. In these three countries the principal axes of elevation are parallel (having the same approximately north-western 
strike); and they are, I believe, due to elevations of an epoch immediately preceding the Trias. These parallel axes affect, 
alike, large groups which are of the Cambrian, Silurian, and Carboniferous periods. 
A single axis of elevation (which I made out in 1833) brings up the old rocks of Charnwood Forest, all of which are 
Cambrian. This fact, considered by itself, proves nothing respecting the epoch of elevation; for any great elevation may 
be expected occasionally to affect any rock of an anterior age. But we can prove that this elevation affects the coal-field 
on the south-west skirt of the Forest, and that it does not affect the Trias. Again, if we follow the axis of elevation 
towards the north-west, beyond the limits of the Forest, we find that it has brought up at a high angle, and dolomitized, 
great broken masses of carboniferous limestone; but it has not affected the position of the Trias, which is horizontal. 
As we trace the line of elevation towards the north-west, its effects gradually disappear, The limestone sweeps round, 
skirting, and forming the geological base of, the Leicestershire coal-field; and as it recovers its natural position it 
ceases to be dolomitized. In one or two places, however, where the beds have been interrupted by minute vertical fissures, 
a mineralizing influence has ascended through the fissures, dolomitized the beds on both sides irregularly, introduced minute 
erystals of galena, and produced miniature representations of the well-known pipe-veins of Derbyshire. 
The Nuneaton coal-field may be described as a very excentric elliptical basin, the major-azis of which is parallel to 
the avis of Charnwood Forest. It is underlaid on the east side (and in one single spot also on the west side) by old (Cam- 
brian?) slate-rocks, which strike and dip exactly with the carboniferous overlying groups. The carboniferous series is over- 
laid by a Permian sandstone, which partakes of the strike and other accidents of the basin on which it rests, and of which 
it forms a part. But all the rocks, whether Cambrian, Carboniferous, or Permian, are skirted and overlaid by horizontal 
deposits of the Triassic marls and sandstones. Here we have a proof that the elevation of the Cambrian rocks did not 
take place till after the Carboniferous and Permian period, and that the elevation was completed immediately before the 
period of the Trias. The facts, so far as they admit of comparison, exactly harmonize with those of Charnwood Forest. 
Respecting the Dudley elevation I have no observations of my own worth recording in this note. The axes of eleva- 
tion (as appears from the memoirs of Sir R. I. Murchison and others who have written on the district) are in a direction 
that is almost mathematically parallel to the axes of Charnwood Forest and the coal-field above described. I believe also, 
from the published descriptions, that the Dudley period of elevation was the same with the periods above noticed: viz. after 
the date of the Permian sandstone, and before the date of the Trias. 
I conclude with this practical remark. While we contend against what we may suppose to be the unphilosophical 
extension of a theory, let us not fall into an opposite error and reject it altogether, even when it helps us to compare and 
marshal facts together. The parallelism of contemporaneous elevations is not a universal truth derived from any known law 
of nature. But, taken with proper caution and proper limitations, it is, I believe, a fact of geology which admits of a 
very extensive practical application, and greatly assists us in grouping together our unconnected phenomena. I believe 
