AUSTEN EXTENSION OF THE COAL-MEASURES. 63 



we may feel sure that a like arrangement of the older strata runs 

 from the valley of the Thames into that of the Kennet ; along this 

 line the coal-measures may he reasonably supposed to have been 

 preserved. 



Guided by the old surface from the Boulonnais eastwards, it is 

 most probable that the breadth of elevated strata south of the above- 

 named line, presented such a series of folds as is now to be seen 

 " entre Sambre et Meuse" and in the Condros, and that this band was 

 much denuded. In this direction, however, from the Boulonnais W., 

 the Carboniferous Limestone contains a subordinate coal-measure 

 series, and the Devonian group presents a like tendency beneath the 

 Ferques limestone. 



To what extent and in what area the denuding process may 

 have extended over the surface of the Palaeozoic strata to the S. of 

 the line of Artois, both in France and England, we have but few 

 data even from speculation : nor is the inquiry of much importance, 

 inasmuch as, should the coal-measures be preserved, they could only 

 be reached beneath enormous thicknesses of secondary strata. The 

 most favourable places for investigation would be points on the S. of 

 the Wealden denudation where the transverse valleys cut deep, and 

 where the Lower Greensand is much reduced in thickness locally. 



The axis of Artois, though a most important feature in its limited 

 extent, is a portion then of a long line of complicated disturbance 

 extending from the western to the mid-European area, the detailed 

 history of which would be a most valuable contribution to physical 

 geology. In the present communication I have only sought to draw 

 attention to just as much as should show its age, its continuity, and 

 its prominence through long periods subsequent to its first pro- 

 duction. 



C. Relations of the overlying Secondary Formations. 



There are doubtless many areas beneath which the coal-measures 

 of our own country may be fairly presumed to extend, but which 

 could only be reached at such vast depths as forbid the prospect of 

 their ever being rendered available : this consideration suggests the 

 third point in the present inquiry, in which the great groups of the 

 geological scale younger than the coal-measures will be taken in 

 ascending order. 



§ 1 . New Red Sandstone. Permian or Triassic. 



An enormous accumulation of conglomerates, sandstones, and clays 

 are interposed between the Palaeozoic rocks of the West of England 

 and the lowest beds of the Oolitic group : it may represent in time 

 either the Permian or more probably the Triassic series, or perhaps 

 both. The local character of the conglomerate shows that it was 

 bounded on the "W. by a terrestrial area. A like assemblage occurs 

 against the E. slope of the old rocks of the Cotentin and Calvados, 



