SOUTH LANCASHIRE, CHESHIRE, AND THE WELSH BORDER. 383 



or coast-ice carried by marine currents in these directions during 

 the period of submergence. 



The former of these hypotheses is opposed by the following facts : — 



(a) The rock surface is not moutonnee on a large scale, and striae 

 are by no means universal, but exceptional, even where Boulder- 

 clay is still in existence. The terminal curvature, like the 

 striae, is of local occurrence. 



(6) The drifts associated with the striae are marine deposits. 



(c) Striae, inclined at various angles to one another, are found 

 not only in the same neighbourhood, but upon the same slab. 



(a) On the first of these points I may remark that though striae 

 are so abundant about Liverpool, and along the valley of the Mersey, 

 they are at present entirely unknown near Chester, though the 

 conditions for their preservation are precisely similar. This fact 

 has been noted also by Mr. Mackintosh *. Within the Welsh border 

 also it may be noticed that though striae in some small areas are 

 abundant, yet it is more common to find the rock-surface, even 

 under undisturbed Boulder-clay, not only not striated, but presenting 

 as ragged a surface as that of a limestone scar exposed to the air. 

 It is, again, a well-known fact that the top of a lead-vein is fre- 

 quently marked by the abundance of pebbles or masses of lead-ore 

 in the drift. So abundant was this ''^ gravel-ore " at Talargoch that 

 the lower bed of the drift was tunnelled in search of it in all 

 directions along the outcrop of the vein, at a depth of about 150-200 

 feet from the surface f. It is clear that these masses of galena are 

 the residue of a considerable thickness of rock that has been removed, 

 and that they have been left in consequence of their high specific 

 gravity. This, however, would hardly have saved them from trans- 

 portation had the district been crossed by an ice-sheet. 



(6) On the marine origin of the drifts of the Lancashire and 

 Cheshire plains and of the Welsh coast and border, there seems to 

 be a general agreement of opinion J. The well-marked stratification 

 of the deposits as a whole and the occurrence of marine shells 

 throughout them seem to point to this conclusion. Though the 

 stratification is scarcely apparent on an inspection of a Boulder- 

 clay section, it becomes so on comparing the records of the great 

 number of shafts and borings that have been made in South Lanca- 

 shire and on the Welsh border. In every case where the drift 

 attains any thickness, as in a preglacial river- valley or the maritime 

 plain of North Flintshire and Denbighshire, it is found to consist 

 of alternations of sheets of Boulder-clay with sand and gravel, the 

 beds running sometimes for a mile or two without interruption. 

 Thin beds of sand may be traced for hundreds of yards in the Boulder- 

 clay, and even the Boulder-clay itself not unfrequently shows a 

 rude separation into more or less stony bands. In one case (the 



* Quart. Jourii. Geol. Soc. vol. xxxv. p. 425 (1870). 



t ' Geology of the Coast adjoining Rhyl, Abergele, and Colwyn ' (Geological 

 Survey Memoir, 1885), p. 47. 



X This opinion is held also by Dr. Hicks. " On some Bone-caves in North 

 Wales," Quart. Journ. Geol. Soc. vol. xlii. p. 16 (1886). 



