NA TURE 



561 



THURSDAY, SEPTEMBER 26, 1878 



THE SUPERFICIAL GEOLOGY OF SOUTH- 

 WEST LANCASHIRE 

 The Superficial Geology of the Country adjoining the 

 Coasts of South-lVesf Lancashire. By C. E, De 

 Ranee, F.G.S. 1877. 



THE memoir of the Geological Surrey by Mr. De 

 Ranee recently published is an interesting contribu- 

 tion to our knowledge of the superficial deposits of the 

 area between the Mersey and the Ribble, which carries 

 the classification of the Cheshire Plain as far to the north 

 as Morecambe Bay. The whole of this district is covered 

 with glacial drift and recent sands, gravels, and peat- 

 bogs, except here and there where the solid rocks come 

 to the surface in the hills. The drift forms an inclined 

 plane dipping from the hills towards the sea, and probably 

 deposited during subsidence upon an old rocky plain of 

 marine denudation, bounded to the east by a line passing 

 from Eccleston to Euxton and Ribchester, and thence 

 through Broughton, Garstang, and Cockerham to the 

 present sea-margin. Were the superficial deposits 

 stripped off this area, the rock-surface would be seen to 

 be not very far from the present sea-level, although the 

 surface of the ground is often 170 feet above it. This 

 plain also dips gently seaward, and has been worn into 

 hollows by the denuding forces before the glacial period. 

 Very- generally it has been cut up into hills and valleys 

 by pre-glacial streams, as, for example, the buried valley 

 of the Mersey described by Mr. Mellard Reade, now 

 filled with 2GO feet of sands, gravels, and clays. 

 These buried valleys may be traced inland, rising 

 nearer to the present surface of the ground as we ap- 

 proach the high ground, until at last their tributaries 

 come to the active surface in the higher hills, and are 

 traversed by the same streams as those now finding their 

 way to the surface, and through the accumulation of 

 drift filling their ancient lower courses. It seems tolerably 

 certain that the hill and valley system of Lancashire and 

 Cheshire was produced by sub-aerial agents before the 

 glacial period, and that the ice merely acted on the solid 

 rock by rounding off and smoothing the raw edges left by 

 the streams and rivers. Indeed, as a rule, it may be said 

 that the relative importance of the agency of rain and 

 rivers, and of ice in scenery making is precisely that of 

 chisel and sand paper, the one carves, while the other 

 rounds off, smooths, and polishes. But whatever view 

 may be held of the cause of this uneven surface below 

 the mantle of the drift, it is a most important fact to be 

 noted, that the surface configuration bears little or no 

 relation to the rock-surface below, as engineers have 

 frequently found out by experience in making reservoirs. 

 In one case, for example, the "puddle trench" had to be 

 carried down 160 feet, so as to render a ravine filled with 

 drift water-tight, and this ravine, with the big boulders at 

 the bottom left in the bed of the stream, by which it was 

 hollowed, was intercepted twice in the course of, the 

 works. 



The drift of the district under consideration is treated 

 by Mr, De Ranee in three divisions, the lower and upper 

 boulder clays, separated from each other by the middle 

 Vol. xviii. — No. 465 



glacial marine sands and gravels. There appears to be 

 no important physical difference between these clays, and 

 their relative age can only be ascertained by their re- 

 lation to the sands above mentioned. This, however, 

 is not an infallible guide, because there are lenticular 

 strata of sand and gravel intercalated here and there in 

 the boulder clays. According to Mr. De Ranee they are 

 absent from the base of the lower boulder clay, a position 

 which Mr. Binney has shown them to occupy in other 

 districts in Lancashire and Cheshire. Our author notices 

 also the glacial striae, roches motitonnees, and the moraines 

 on the higher grounds overlooking his area, and points 

 out very justly (p. 46) that " the till " and " lower moraine 

 drift " of other districts may have been formed at the same 

 time that the lower boulder clay was being accumulated. 

 It may also be pointed out that the local glaciation of 

 North Wales and of the Pennine chain, and of the hills 

 of Cumberland may have been produced while the upper 

 boulder clay was being formed. Nevertheless, we cannot 

 obtain an accurate idea of the relation of the various 

 glacial phenomena to one another in point of time in 

 different parts of Britain, until we can ascertain the 

 sequence and extent of the changes of level, which has not 

 as yet been made out. To my mind three great changes 

 only have been proved to have taken place over a wide 

 area : two periods when Britain stood at a higher level 

 than it does now, with an intervening period, during 

 which the region north of the lower Thames and Severn 

 was submerged to a depth of 1,200 to 1,500 feet on the 

 flanks of Snowdon. There were three corresponding 

 elimatal changes, the first period of elevation being 

 marked by a very low temperature ; the second, or that 

 of depression, by temperate conditions ; and the third or 

 last period of elevation being also marked by severe 

 elimatal conditions. It is obvious that, during changes 

 such as these, the sands, gravels, and clays, termed 

 "glacial drift," would be so extremely complicated 

 and so various in different places, that it is difficult, if 

 not impossible, to ascertain the contemporaneity of the 

 more minute sub-divisions of the glacial strata. While 

 sands and shingle were being accumulated along the 

 coast-line, melting icebergs were dropping their burdens 

 to form boulder-clays in the adjacent sea, and on the 

 land the moraines of the retreating glacier were being 

 heaped together, or the advancing glacier was ploughing 

 its way downwards. All these operations were going on 

 simultaneously in different parts of the glacial area of 

 Great Britain, and their results are rendered infinitely 

 more complex by the oscillations of the level of the 

 land, which may have been local, and by changes 

 of climate as yet imperfectly understood. - From 

 these considerations it is evident that the clays and 

 shingles and sands cannot be severally classified toge- 

 ther, excepting in the strict homotaxial sense, and 

 apart from all ideas of contemporaneity, and that the 

 sequence of the minute divisions of the glacial period in 

 Scotland, published by Dr. James Geikie in his able 

 work, and based upon the relation of clays to sands and 

 gravels, cannot in the nature of things apply to Lan- _ 

 eashire, or any other areas beyond Scotland. Mr. De^ 

 Ranee has acted prudently in confining his attention to 

 the drifts of the area treated in the memoir without 

 dealing with the general question, which, to my mind, is 



