to 
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bo 
MR. A. STRAHAN ON THE ORIGIN OF [May 1902, 
EXPLANATION OF PLATE V. 
Map of South Wales and of a portion of South-Western England, on the 
scale of 30 miles to the inch, illustrating the relation of the water-partings 
to the geological structure. 
The main water-parting of South Wales, and the limits of the basing of the 
Thames and Frome, are shown by thick broken lines ; other water-partings being 
indicated by heavy dotted lines. 
Strong black lines indicate the Caledonian disturbances of South Wales 
referred to in the text :— 
A = The Llandilo disturbance. D = The Cribarth disturbance. 
B = The Cennen do. KE = The Vale-of-Neath do. 
C = The Tair-Carn do. { 
Discussion. 
Prof. Groom said that he had listened with great interest to 
the paper, since it dealt with an area with part of which he was 
familiar. He regretted, however, that the term ‘ Caledonian’ 
had not been used in conformity with its original application, and 
had been employed to designate movements which had taken place 
in a different district and at a different time from those which gave 
rise to the ‘Caledonian Range’ of Suess. This, he was afraid, might 
lead to confusion. , 
As to the substance of the paper, while there was much in it 
with which he could agree, he felt great hesitation in accepting the 
Author’s conclusions on one important point. According to the 
Author, the movements that gave rise to the south-westerly trend 
of the rocks in Central Wales were of later date than those that 
produced the Armorican branch of the Hercynian system. The 
speaker thought, however, that the evidence available tended the 
other way. ‘The general progress of folding in Britain, as on the 
Continent, appeared to have been from the north-west; and the dis- 
appearance of the north-easterly and south-westerly folds in the 
southern parts of Wales and Ireland along the line of the Armorican 
folds, seemed to be best explained by supposing the latter to have 
been superimposed on the former. Moreover, there was direct 
evidence that the folding termed Caledonian by the Author had 
made very considerable progress in pre-Carboniferous times. Thus in 
Radnorshire, and farther north-east in Shropshire, important move- 
ments, during the Llandovery Period, appeared to have already 
impressed on the beds a south-westerly trend. Further movements 
had probably taken place in later Silurian times, and again before 
the deposition of the so-called Upper Old Red Sandstone and Carboni- 
ferous Limestone. In the Berwyn Hills, indeed, according to recent 
investigations by Mr. Philip Lake and the speaker, the folding in 
pre-Carboniferous times had been so great that, at a time when the 
Carboniferous Limestone was horizontal, the underlying beds already 
dipped at 70° or more. Here, as also in the neighbourhood of 
Llandilo, the creep had been from the north-west, as the Author had 
maintained forthe latter area; and in both cases inversion of the beds 
occurred on the south-east. Doubtless later movements in the same 
