September 9, 1910] 



SCIENCE 



331 



their movements have been correlated by 

 Professor J. Geikie with those already 

 mentioned in the Alps. Into that very 

 difficult question I must not enter; for my 

 present purpose it is enough to say that in 

 early Pleistocene times glaciers undoubt- 

 edly existed in the mountain districts of 

 Britain and even formed piedmont ice- 

 sheets on the lowlands. On the west side 

 of England, smoothed and striated rocks 

 have been observed near Liverpool, which 

 can hardly be due to the movements of 

 shore-ice, and at Little Crosby a consider- 

 able surface has been cleared from the 

 overlying boulder clay by the exertions of 

 the late Mr. T. M. Reade and his son, Mr. 

 A. Lyell Reade. But, so far as I am 

 aware, rocks thus affected have not yet 

 been discovered in the Wirral peninsula. 

 On the eastern side of England similar 

 markings have been found down to the 

 coast of Durham, but a more southern ex- 

 tension of land ice can not be taken for 

 granted. In this direction, however, so 

 far as the tidal valley of the Thames, and 

 in corresponding parts of the central and 

 western lowlands, certain deposits occur 

 which, though to a great extent of glacial 

 origin, are in many respects different from 

 those left by land ice in the Alpine regions 

 and in northern America. 



They present us with problems the na- 

 ture of which may be inferred from a 

 brief statement of facts. On the Norfolk 

 coast we find the glacial drifts resting, 

 sometimes on the chalk, sometimes on 

 strata of very late Pliocene or early PleLs- 

 toeene age. The latter show that in their- 

 time the ' strand-line must have oscillated 

 slightly on either side of its present level. 

 The earliest of the glacial deposits, called 

 the Cromer Till and Contorted Drift, pre- 

 sents its most remarkable development in 

 the cliffs on either side of that town. Here 

 it consi.sts of boulder clays and alternating 



beds of sand and clay; the first-named, 

 two or three in number, somewhat limited 

 in extent, and rather lenticular in form, 

 are slightly sandy clays, full of pieces of 

 chalk, flint and other kinds of rock, some 

 of the last having traveled from long dis- 

 tances. Yet more remarkable are the huge 

 erratics of chalk, in the neighboriiood of 

 which the sands and clays exhibit extra- 

 ordinary contortions. Like the beds of till, 

 they have not been found verj^ far inland, 

 for there the group appears as a whole to 

 be represented by a stony loam, resemb- 

 ling a mixture of the sandy and clayey 

 material, and this is restricted to a zone 

 some twenty miles wide, bordering the 

 coast of Norfolk and Suffolk; not extend- 

 ing south of the latter country, but being 

 probably represented to the north of the 

 Humber. Above these a group of false- 

 bedded sands and gravels, variable in 

 thickness and character — the Mid-glacial 

 Sands of Searles V. Wood and F. W. 

 Harmer. They extend over a wider area, 

 and may be traced, according to some geol- 

 ogists, nearly to the western side of Eng- 

 land, rising in that direction to a greater 

 height above sea-level. But as it is impos- 

 sible to prove that all isolated patches of 

 these materials are identical in age, we can 

 only be certain that some of them are older 

 than the next deposit, a boulder clay, 

 which extends over a large part of the low- 

 lands in the eastern coimties. This has 

 a general resemblance to the Cromer Till, 

 but its matrix is rather more clayey and is 

 variable in color. In the north of York- 

 shire, as well as on the seaward side of the 

 Lincolnshire wolds, it is generall}^ brown- 

 ish or purplish, but ou their western side 

 and as far as the clay goes to the south it is 

 some shade of gray. Near to these wolds, 

 in mid-Norfolk, and on the northern mar- 

 gin of Suffolk, it has a whitish tint, owing 

 to the abundance of comminuted chalk. 



