AUSTEN EXTENSION OF THE COAL-MEASURES. 43 



having some such positions as above described ; and, as there is an 

 exact relation and balance between the amount of sedimentary matter 

 and the coast-line from which it is derived, the extent and dimensions 

 of the palaeozoic masses afford an indication of how vast a region that 

 was which has disappeared. 



The lines of saliency and depression which have subsequently 

 shaped out and formed our present Western European areas have been 

 mostly transverse to the direction of the original lines. With refer- 

 ence to the present inquiry, we have only to compare the palaeozoic 

 region which extends south from the Department of the Manche with 

 that of our own western counties, to ascertain what was the character 

 of the changes of the middle and lower palaeozoic periods. 



If we take zoological considerations as a guide, the southernmost of 

 these areas seems to have been subject to fewer changes favourable 

 to the immigration of new and successive occupants than the Silurian 

 region of Sir R. Murchison was. The nature of the difference is this, 

 the sequence of animal life was not the same through the same periods 

 of time over adjoining areas. The geographical variation in the marine 

 fauna was, perhaps, greater during the palaeozoic period than it is at 

 present ; but making every allowance for this, it will be found insuf- 

 ficient to meet the nature of the change which takes place. 



I would indicate as an inquiry to be made, — why it is that the 

 lower palaeozoic group of Western France, as the slates of Parennes, 

 and their equivalents, should differ so materially, as to their contents, 

 from the Llandeilo and Bala groups, of which they are received as 

 the synchronous products. Ascending higher in the same French 

 series, the want of parallelism with our own becomes still more 

 striking ; and in estimating the value of this with reference to the 

 restoration of any salient lines, it must be remembered, that the 

 French sections show perfect continuity throughout*, and that the 

 value of this evidence over-rides all other in a question of chrono- 

 logical sequence ; and also that the palaeozoic series of western France, 

 as a whole, is synchronous with that of the British area. 



In France the palaeozoic series consists of a Lower Silurian, an 

 Eifelian, and finally of a Carboniferous division, which last commences 

 with a group corresponding to the Marwood beds, as in the Boulon- 

 nais. The observations of Mr. Haughton enable us to extend the 

 area of like conditions for the lower carboniferous group as far as 

 Anglesea. 



In the total absence of any direct physical evidence, we are not 

 warranted in supposing that any portions are relatively wanting 

 between the palaeozoic groups of Western France and England ; but 

 merely that in parts, and from local causes, what are true equivalents 

 are differently represented. That which we recognize in the English 

 series as an Upper Silurian fauna does not seem to have found ad- 

 mission into the area of the palaeozoic seas of France, nor indeed into 

 those of southern and eastern Europe. It may be suggested, perhaps, 

 that the oceanic region then may have been one and the same, but 



* Bull. Geol. Soc. Fr. vol. ii. pi. U. 



