000 J. J. Harris Teall—Effect of Earth-Movements. 
c. Movements due to lateral pressure which produce a folding or 
contortion of the stratified rocks along certain definite lines. 
Tt must be understood that this classification is proposed merely 
for the purpose of aiding description, and not because I believe that 
these three classes of movements are radically distinct. I have little 
doubt that they are very closely connected and that the nature of 
this connexion will at some future time be fully established. In the 
present communication I propose to refer to those movements of the 
third class which have affected the stratified rocks of Great Britain 
and Ireland, to discuss their geological age, and to describe the 
effects they have produced on the actual structure of our country. 
I have nothing new in the shape of facts to offer; my object is 
merely to collect together the knowledge which various workers in 
the field of geology have accumulated with reference to this interest- 
ing topic, and in conclusion to suggest an extension of what may be 
fairly called the American theory of the origin of mountains to the 
subject in question. 
The earliest earth movement of which we have direct evidence 
is one which affected the Pre-Cambrian rocks of the N.W. of Scot- 
land and §.W. of Wales. In the former locality these rocks consist 
of highly crystalline gneiss, with occasional beds of limestone and 
ironstone, evidently the metamorphosed representatives of marine 
formations. They are now arranged in strata dipping towards the 
N.E. and §.W., in such a way as to show that subsequent to their 
formation, and probably during the time when the metamorphism 
was produced, they were subjected to forces which contorted the 
rocks along axes running N.W. and 8.E. In the §.W. of W ales, in 
Pembrokeshire, rocks similarly related to the Cambrian occur. 
These have been divided by Dr. Hicks into two groups,’ to the 
earlier of which he gives the name Dimetian, and to the later 
Pebidean. 
The lower, or Dimetian series consists of compact quartziferous 
beds and altered shales and limestones, which strike in a N.W. and 
SE. direction, thus showing, in all probability, that they were 
affected by the same earth movements as the homotaxial beds of the 
N.W. of Scotland and the Hebrides. The upper or Pebidean series 
consists of altered conglomerates and shales, the pebbles of the con- 
glomerate having been derived from the earlier formation. These 
beds are entirely unconformable to the Dimetian series, and strike 
in a direction W.S.W. and E.N.E. The same old Pre-Cambrian 
rocks as those to which Dr. Hicks has given the term Dimetian in all 
probability again come to the surface in the Malvern Hills, where 
they consist of regularly stratified gneiss, having the usual strike. 
Tf the newer formations which cover the country at all those 
points intermediate between the localities above mentioned could be 
removed, we should find in all probability that these early Pre- 
Cambrian rocks are very widely distributed, even at present. During | 
the Cambrian period they formed the superficial crust of the earth, 
1 Dr. Hicks now divides the Pre-Cambrian rocks into three groups, Dimetian, 
Aryonian, and Pebidean. 
