NORTH- WEST OF ENGLAND AND NORTH WALES. 125 



Smaller boulders, are often ground to a perfectly true plane, and 

 sometimes without striations. In others the stone presents several 

 distinct planes or facets with striations meeting in a herring-hone 

 fashion ; others are irregular in form and indefinitely scratched all 

 over as if bumped about, or rolled over, under ice. Sometimes boul- 

 ders occur aggregated in nests or pockets in the clay. 



It is quite evident that these stones have never been disturbed 

 since they were dropped in the mud of a glacial sea *. 



The proportion of the contained stones to the bulk of the deposit 

 varies very considerably. Some of the clays are decidedly stony ; and 

 others consist of a great mass of unctuous clay with very few stones, 

 but with a large percentage of fine gravel intimately intermixed with 

 it. Probably half of the stones taken out of the clays in the neigh- 

 bourhood of Liverpool used for brick-making are more less scratched ; 

 and it is worthy of remark that by far the larger proportion of the ex- 

 amples I have collected of specially well glaciated stones are Silurian 

 grits or other old rocks from the mountain-districts. Eutinbeds of 

 gravel and sand the stones are usually rounded. This, however, can 

 hardly be an evidence of an interglacial climate ; for we find in many 

 cases, as I have detailed, that the lower and harder beds of the clay often, 

 nay, generally contain more rolled stones than the upper or middle. 

 Such is the case at Dawpool ; and itwas so in the Atlantic Docks, Liver- 

 pool. At Blackpool, on the contrary, according to Binney, the lower 

 and harder beds contain the greatest number of striated stones. 



It is therefore clear that these distinctions cannot indicate climatic 

 differences. 



And if this be admitted, can we on these grounds consider the 

 lower bed of Boulder-clay as a geological subdivision ? The true ex- 

 planation seems to be that these stones have been rolled on the beach 

 before being finally deposited on the muddy bottom of the Glacial sea. 

 When beds consist solely of gravel, boulders, and shingle, that, in itself, 

 is a proof that either tidal currents or shore-conditions have prevailed 

 in the places where they have been laid down, or that they have 

 been at a depth no greater than where the wind waves can act upon 

 and move them. 



The absence of stones in some of the sand, as in the section de- 

 scribed by Mr. Shone, near Chester, it appears to me, can be accounted 

 for in this manner, Beds of clay must necessarily be very slow 

 accumulations. Beds of sand, on the contrary, within reach of the tide 

 are constantly moving ; as an illustration, the banks and channels in 

 the estuary of the Mersey are constantly being surveyed aud the chan- 

 ges marked by buoys by the marine surveyors. 



Hundreds of thousands of tons will be shifted by a single gale. 

 If there were floating ice conveying stones and depositing these in the 

 estuary now, what would be the effect ? They would be sorted by 

 the currents, we should have shingle in one place, sand only in another, 



* Dr. James Greikie has expressed the opinion that these deposits are sea- 

 bottoms ploughed up by land-ice (" The Intercrossing of Erratics," reprint from 

 the ' Scottish Naturalist '). 



