1869.] MACKIITTOSH LANCASH.IEE AKD CTTMBERLAND DEIFTS. 419 



shaves away the edges and grinds down the faces of stratified rock- 

 masses. It can produce an undulating surface ; but the vertical ex- 

 tent of the heights and hollows must be small in comparison with 

 their breadth. It cannot scoop out small deep basins, deep grooves 

 pointing in various directions, and, least of all, funnel-shaped holes 

 running down through slabs of rock. Water finding its way through 

 cracks in glaciers may perhaps produce all these forms of rock- 

 surface in valleys ; but on the summits of limestone hills such pheno- 

 mena must be referred to the action of rain or sea-waves. Rain (as 

 I have already shown in this Journal*) cannot grind rock-surfaces 

 so as to leave smooth curvilinear hoUows cutting continuously through 

 hard and soft parts of the stone ; but it must communicate a rough 

 irregular surface minutely corresponding to variations in lithological 

 structure or composition. 



h. Roch-worTc of BirTcrigg Moor and Ham^sfell. — On the rocky 

 summit called Birkrigg Moor near Ulverstone, and on the still higher 

 eminence called Hampsfell, near Grange, rain is now clearly break- 

 ing up everything like regularity of form. It is converting pre- 

 viously smooth basins into rough, pitted, and fretted depressions, and 

 smooth grooves into jagged stone gutters. But these hills, especially 

 the borders of Birkrigg Moor, present proofs of the most undeniable 

 kind that no agent has formed the smooth and regular rockwork 

 since the Glacial period. The basined, grooved, and fanneUed sur- 

 faces of limestone rock run under drift. without any change of form, 

 excepting that, under damp clay, in many places the surface has been 

 roughened. The connexion between sculptured limestone rock- 

 surfaces and drifts in this district offers a new field of research to 

 the geologist. So far as I have observed, the hollows must nearly 

 all have been ground out before the deposition of the Upper Boulder- 

 clay . They not only run under a loose reddish drift on the borders 

 of Birkrigg Moor, but under the decided upper drift further west- 

 ward ; and sculptured boulders may be seen buried in this drift. 

 Large sculptured boulders on Stainton Green (see sequel) present 

 grooves and other hollows running continuously from the upper to 

 the under surface, and along the latter down into the matrix of red 

 loamf. The semi-island of Dunnerholme (see sequel) is covered 

 with an upper drift which rests on sculptured limestone — the rounded 

 stones of this drift still sticking in the funnel-shaj)ed holes they ap- 

 parently helped to gn'nd out. But the period of the sculpturing 

 of the limestone rocks must be carried still further back ; for sculp- 

 tured boulders may be found in hard Lower Boulder-clay, though in 

 this clay the sculptured surface, the typical form of which can be at 

 once recognized, has become irregularly pitted. Under the Lower 

 Boulder- clay the rock-surfaces often present the same general forms, 

 though in most places they have become fretted through some kind 

 of chemical action, probably intensified by the humus carried down 

 from the surface by rain-water percolating through crevices. 



* Quart. Journ. Geol. Soc. vol. xxiv. pp. 277 & 278. 



t On the sea-shore between Morecambe and Carnforth I have seen sculptured 

 limestone boulders fixed in what looked like Lower Boulder-clay. 



