334 PEOCEEDINGS OF THE GEOLOGICAL SOCIETY. [April 8, 



in Europe by the period of the Huschelkalk. The amount of material 

 swept away in Lancashire at this period was probably not great; 

 but of the fact itself there is the most positive evidence, as the 

 basement-beds of the Keuper rest unconformably on an eroded sur- 

 face of the Bunter Sandstone at Ormskirk, Liverpool, and Birken- 

 head. 



Fourth Period. — The long ages of subsidence and submergence of 

 the Bed Marl, Lias, and the Jurassic groups elapsed, to the close of 

 which, as it ^seems to me, w^e must refer the system of north- 

 westerly faults which traverse the Carboniferous, Permian, and 

 Triassic formations. Along with the production of these fractures, 

 which displaced the strata to the extent of 3000 or 4000 feet in 

 some places, there must have been a corresponding amount of carry- 

 ing away of materials. The result of this, and probably of other more 

 recent denudations, has been almost to obliterate all surface indica- 

 tions of these enormous vertical displacements, as in the case of the 

 great Irwell-valley fault. . In other cases, where the features of 

 the ground do happen to indicate the lines of fracture, as in the 

 case of the Up-HoUand fault, it is only to the extent of a few hun- 

 dred feet, while the displacement of the beds may amount to as many 

 thousands. 



Fiftli Period. — The next period of denudation of wliich we have 

 any evidence in this part of the country was that immediately 

 antecedent to the period of the Lower Boulder- clay, or Till. In 

 this instance there was probably a combination of ice- action, sea- 

 action, and rain- and river- action, as the rocks at Liverpool, Hor- 

 wich, Whalley, Clitheroe, &c. afford evidence of glaciation below 

 the Boulder-clay. To this period many of the primary valleys and 

 other features of the surface are to be referred. 



Sioctli Period. — The beds of sand and gravel which lie between 

 the Lower and Upper Boulder-clays afford most clear evidence of 

 extensive erosion and denudation before the deposition of the Upper 

 Till upon them, as I have shown in my papers on the drift-deposits of 

 Lancashire and Cheshire. To what extent this local erosion ex- 

 tended to the older formations it is impossible to say ; but the effect 

 was probably small. At the same time, in a summary of this kind, 

 the occurrence of this period of denudation ought not to be passed 

 over in silence. 



Seventh Period. — The seventh and last period was that which 

 ensued at the close of the Glacial epoch, and is still in existence. To 

 this period is to be referred the channelling out of all the secondary 

 valleys by " atmospheric denudation," and the modification by the 

 same agency of all the physical features. Many of these valleys 

 have been hollowed out in the lines of older valleys which had been 

 partially filled in with drift- deposits, producing the phenomena of 

 ^' valleys within valleys " *. E'o one, indeed, can traverse the hills of 



">" A term which I have employed to describe a class of physical features not 

 uncommon in the Pennine chain, the Cotteswold Hills, and other districts. See 

 my paper on " Modern Views of Denudation," in the ' Popular Science Eeview,' 

 October 1866. 



