EEOSION OF THE GLACIAL DKIFT. 99 



The soil A-A rested on the undulations of the Upper Boulder 

 Clay B-B, and the latter on the undulating surface of the Middle 

 Sands and Gravels C-C, whilst a curved layer of local pebbles of 

 Bunter Sandstone (D) followed the curvature of the beds A, B, C. 

 These lines of curvature, so frequent at the junction between the 

 Upper Boulder Clay and the Middle Sands and Gravels, have been 

 often, I think, erroneously interpreted as evidences of unconformity, 

 contemporary erosion, or contortion. I venture to express the 

 opinion that such appearances are in the vast majority of instances 

 the results of the subterranean erosion of the heterogeneous deposits 

 of the Glacial Drift. 



While I have so far confined myself to the subterranean erosion 

 of the Drift sands and gravels, I do not wish to be understood to 

 limit its action to these deposits. I believe subterranean erosion to 

 be a factor capable of explaining many difficult problems not alone 

 in the present but also in the past, especially with regard to the 

 formation of Coal-beds. 



If it be established that the Drift sands and gravels com- 

 monly occurring under the Upper Boulder Clay have been subject 

 to subterranean erosion, thereby causing a lateral subsidence 

 of the clay, it follows that in low-lying districts submerged 

 Peat- and Porest-beds would be the natural consequence. Such 

 conditions do prevail along the low belt of land forming the 

 coast-line of the N.W. of England and "Wales from Lancaster to 

 Great Orme's Head, and submerged Peat- and Porest-beds are 

 matters of common occurrence. After storms remnants of such 

 beds are often laid bare between high- and low-water marks along 

 the whole of this coast, and between the Bibble and the Dee 

 these exposures have been watched and noted by careful observers 

 for many years. Perhaps the best sections are those exposed from 

 time to time between the Dee and the Mersey, on the Cheshire 

 shore at Leasowe. 



Mr. G. H. Morton, in the first edition (1863) of his ' Geology 

 of the Country around Liverpool,' gives a section of the Peat- and 

 Porest-beds at the locality mentioned.^ 



The strong resemblance which Mr. Morton remarks between the 

 Peat- and Forest-beds and the Coal Measures may be due to like 

 causes in the past and present. In other words, what will explain 

 the origin of submerged Peat- and Porest-beds may also be helpful 

 in clearing away many difficulties in connexion with the origin of 

 Coal-beds. Mr. Morton further states that, on '' approaching the 

 embankment from Dove Point, the two lower old Porest-beds 

 gradually amalgamate, and then both are represented by one carbo- 

 niferous bed, the three feet of silt between having thinned out 

 until lost." 



The section given by Mr. Morton in his admirable second edition 

 (1891) of ' The Geology of the Country around Liverpool,' on the 

 Manchester Ship Canal between EUesmere Port and Ince Perry, 



1 O'p. cit. p. 48. 



