TRANSACTIONS OF SECTION C, t ti) 



10. On the pre-Glacial Form of the Ground in Lancashire and Cheshire. 

 By C. E. De Range, F.G.S.,of H.M. Geol. Siavey. 



The author arrived at the following conclusions : — 



1. The carving out of rock valleys has been mainly due to fluviatile action, 

 operating before the Glacial period, when the land stood at least 300 feet higher 

 above the sea-level than it does at present. 



2. The valleys which lie below sea-level are entirely choked up by glacial 

 drift, and absolutely concealed, and but for extensive boring operations their 

 presence would never have been suspected. 



3. The materials and irregular alternation of sequence of glacial material in 

 the infra-sea-level valleys are identical with the character of the deposits above the 

 sea-level. 



4. There is now ample proof that these ' choked-up ' valleys extend a con- 

 siderable distance under the Irish Sea. 



6. The glacial deposits extend up to 1,260 feet on the slopes of the Cumberland, 

 Lancashire, Cheshire, and Carnarvonshire hills, margined by erratic blocks of large 

 size that extend further and rise higher than the drift, and form a ' fringe ' deposit, 

 such as has been described in the United States, marking the limit of the margin 

 of the ice-sheet, the highest boulder in Cheshire occurring at 1,364 feet. 



6. The glacial deposits consist of (a) tough dark till with local fragments in 

 the neighbourhood of shales, especially of Coal-measure age ; {b) clay with local 

 angular fragments of sandstone and a few erratic pebbles ; (c) boulder clay, a red 

 or reddish-brown clay passing into marl, which when washed contains rounded and 

 glaciated grains of sand, of erratic origin, which are microscopic specimens of like 

 shape and like origin to the boulders that occur in the clay, and which range in 

 size up to 12 feet ; (d) sands and gravels : these contain fragments of marine shells, 

 up to 1,260 feet : these fragments are water-worn, often striated, and are themselves 

 erratics. The author has never found two valves of a bivalve united ; the species are 

 representative of different * depth zones,' and univalves contain sand or silt of a dif- 

 ferent character from the sand by which they are surrounded. The sands also contain 

 fragments of all sizes of boulder clay, often angular and ragged, as if torn off ; the 

 sands are generally current-bedded, but often show distinct signs of ' fluxion struc- 

 ture,' and have been apparently formed partly in freshwater lakes and partly xinder 

 land-ice. 



7. Deep borings and sinkings invariably give a series of these clays and sands, 

 often repeated eight or ten times over ; consequently it is obvious that, though a 

 bed of sand in one area may divide a bed of clay into an ' upper ' and a ' lower 

 boulder clay,' it is not only not certain that such upper boulder clay is on the same 

 horizon as the local upper boulder clay in an adjacent area, but it is exceedingly 

 improbable that it shoidd be so. 



8. The average thickness of the alternations of boulder clay and sands is 

 such that, as a rule, the deepest Lancashire and Cheshire drift valleys of 80 to 150 

 feet disclose sections of the first three members of the series, and fully justify 

 Professor Hull's classification of an upper and lower boulder clay, divided by a 

 middle sand and gravel, often called the 'middle drift.' Had the beds been 

 thinner, the true succession would have at once been recognised as far more 

 numerous than the three-fold sequence observed by Professor Hull. 



9. The interior composition of a glacial drift mound, or of a drift plateau 

 between two valleys, is nearly always delusive as regards the surface indications. 

 A constant arrangement of the surface deposit in a drift mound is a base of boulder 

 clay, a strip of sand, a wide slope of boiilder clay, and a crest or ridge of sands 

 and gravels. As a rule it is at once obvious that the clay on the upper slope i.s 

 overlying the sand and gravel of the ridge, but as a ride it is far less obvious that 

 the clay at the foot of the slope is really not underlying, as at first sight seems 

 apparent, but overlying the upper boulder clay, and is ' plastered ' over the sands 

 and gravels of the mounds, which resemble in section the coats of an onion — beds 

 of variable thickness of boulder clay surrounding and washing an internal core of 

 fiand and gravel. 



