Ixxxii PROCEEDINGS OF THE GEOLOGICAL SOCIETY. 



In S. Wales and the adjoining counties of England, the directions 

 of the lines of elevation vary from a few degrees S. of E. to several 

 degrees N. of N.E., and, moreover, all the lines between Cardigan Bay 

 and the anticlinal ridge of the Towy ai-e regularly and continuously 

 curved. To account for these anomalies our author has recourse to 

 the anterior systems of Finisterre, JFestmoreland, the Ballons, and 

 Forez, combined with that of the Netherlands, the one we are con- 

 sidering. The influence of the system of Finisterre, supposed to be 

 ante-silurian, in this region is merely hypothetical, and I have proved 

 that the movements which produced the other three anterior systems 

 (all of which are post-silurian) must here have been inappreciable, 

 because the Silurian beds must have remained sensibly horizontal 

 till the disruption of the Coal-measures. There coidd not, therefore, 

 be any pre-existing dip of suflicieut amount to modify materially, 

 accorduig to the first of the above-mentioned suppositions, the 

 powerful movement which elevated S. Wales and extended, as I con- 

 ceive, throughout the whole of the Principality and the neighbouring 

 distiict. 



When a mixed system, or one whose direction is borrowed from a 

 previous one, is supposed to arise from a modified action of the cause 

 producmg it, according to the second of the above-mentioned suppo- 

 sitions, we must assume lines of elevation to be more easily produced 

 in the directions of pre-existing lines than in any other, or, in other 

 words, we assume those lines to be lines of least resistance. If the 

 acting cause be a force extending the mass acted on, and the pre- 

 existmg lines have originated in fissures, the above assumption A\ill 

 necessarily be true, and I have elsewhere investigated the influence 

 of such pre-existing fissures on the formation of subsequent ones. 

 But when the acting force is a compressing one, and the previous 

 lines of elevation have originated in comjrression, it by no means 

 follows that those lines vi\[\ be lines of least resistance to a subsequent 

 compressing force. It is just as possible, I conceive, that they might 

 become lines of greatest resistance. Any conclusions deduced from 

 the assumption of their being lines of least resistance could not, I 

 think, be satisfactory. I cannot, therefore, attribute any material 

 influence of this kind on the great elevatory movement of this di- 

 strict, to any anterior recognizable movement which can have taken 

 place in it, and I cannot, therefore, regard these explanations of the 

 phsenomena of elevation of S. Wales as at all satisfactory. 



The tenth system of our author is that of the Rhine. Its epoch 

 is immediately anterior to the Trias, and appears to be very well 

 defined by the phsenomena in the Vosges Mountains, on which the 

 system is fomided. It would seem, at least, that, in the continental 

 localities where it is supposed to manifest itself, its epoch caimot be 

 later than that just mentioned. Its orientation in the west of England 

 is about N. 13° E. M. de Beaumont supposes it traceable in the 

 northern part of the Dudley coal-field, from the direction of which, 

 however, it differs by about 9° ; and, moreover, the principal disturb- 

 ance there has been proved, as I have already shown (p. Ixxvi), to 

 have been posterior to a large part of the Trias, at least, and the 



