Ixxviii PROCEEDINGS OF THE GEOLOGICAL SOCIETY. 



strike varying in direction from a few degrees E. of N. on the southern, 

 to N.W. on the northern part of their range. I am not acquainted 

 with the evidence hy which the movements which have affected them 

 may he dated. 



The last Coal-field I shall notice is that of S. Wales. The date 

 of its great movement, if we are to refer its dislocations to one such 

 movement alone, is considered to be the sam.e as that of the Bristol 

 coal-field as determined by means of the Dolomitic Conglomerate. If 

 we adhere to the opinion that the age of the Conglomerate is the 

 same as that of the JMagnesian Limestone of the northern counties, 

 we have no evidence to separate the epoch of the movement in that 

 region, of which the characteristic dhection is N. and S., from that 

 of S. Wales in which the direction is E. and W. If, on the contrary, 

 we adopt the "\iew of M. de Beaumont and assign the Conglomerate to 

 the commencement of the Triassic period, we have no means (as above 

 remarked) of distinguishing its epoch from movements at Dudley or 

 Coalbrook Dale producing nearly northerly or north-easterly direc- 

 tions. In either case, moreover, this epoch cannot be separated from 

 that of the Bristol district, in the northern and larger portion of 

 which the direction is N. and S. 



Let us now return to our author's systems, and examine their 

 applicability to the phsenomena of the districts which we have briefly 

 passed in review. His first four systems, those of La Vendee, 

 Finisterre, Longmynd, and Morbihan, are all regarded as probably 

 antesilurian, but so far from its being possible to prove the different 

 lines of elevation referred to them to be respectively contemporaneous, 

 the chronological order of the systems themselves cannot be deter- 

 mined with any certainty. They can only, therefore, be severally 

 regarded as systems of parallel lines, the contemporaneity of which 

 admits of no independent proof. I may also observe, that the 

 Longmynd has been, I think, unhappily chosen as the type of one of * 

 these systems. Those rocks appear to be referable to the lower part 

 of the series of N. Wales, where the strike of the Longmynd system 

 never presents itself. The district of Longmynd too is of small extent, 

 and lies upon a line of volcanic eruption running in a N.E. and S.W. 

 direction. Volcanic action appears to have been frequent and violent 

 there, and it is probably to that action that the highly disturbed state 

 of the Longmynd beds and the abnormal direction of their strike are 

 to be attributed. This does not prove the non-existence of the system 

 elsewhere, but I am persuaded that the Longmynd has no claim to 

 be made the base on which it ought to rest. The other three of these 

 systems are founded on observations made in North-western France. 



The next system recognized by our author is that of Westmore- 

 land. He appears to consider the Tilestone as equivalent to the 

 lower division of the Devonian series, more developed in certain con- 

 tinental localities. The epoch of this system, therefore, supposed to 

 be immediately after the Tilestone, corresponds, according to this 

 view, to the middle of the Devonian and not to the conclusion of the 

 Silurian period, this latter epoch not being recognized as one of those 

 at which any system has originated. The same remark applies to the 



