486 Horace B. Woodward — The Chalhy Boulder-clay. 



Northamptonshire, and in certain Midland areas, there is a local 

 absence of Boulder-clay and of signs of glaciation — an absence not 

 always to be attributed to subsequent denudation, but rather sug- 

 gesting that the margin of the ice-sheet was prolonged here and 

 there into tongues or broad lobes, as in the vale of Moreton, the low- 

 grounds near Buckingham, and the lower areas of Chalk and Tertiary 

 strata in Hertfordshire. 



Prior to the formation of the Chalky Boulder-clay in the more 

 central portions of England, we may picture an area whose main 

 features did not differ very largely from those of the present time. 

 The stonebrash hills, in the now glaciated tracts, may have stood out 

 somewhat more prominently from the clay vales in the Jurassic areas, 

 and the country was thickly coated with weathered rock or rubble. 

 The Chalk areas were more extensively covered with clay-with-flints, 

 and with outliers of Tertiary clays, sands, and gravels ; while, over 

 the barer tracts of Chalk, the rock itself was much broken up at the 

 surface, and the loosened blocks were in places weathered into 

 a somewhat rubbly form. Hence the greater portion of the land was 

 covered with disintegrated rock and loose superficial strata, such as 

 would readily be frozen into the base of a sedentary ice-sheet, if 

 formed, as in North America, in 'the way so clearly depicted by 

 Mr. W. 0. Crosby.i 



That the contents of the Chalky Boulder-clay vary to a noticeable 

 extent in accordance with the nature of the strata over which the ice 

 passed, is a well-established fact : nevertheless, the Boulder-clay 

 maintains over a wide area its characteristic chalky ingredients. 



It thus appears remarkably uniform in character in its extent from 

 Norfolk to Essex, and from the Eastern Counties to Northamptonshire 

 and Buckinghamshire — a feature mainly due to its abundant chalk 

 and flint. More chalky in West Norfolk, it is more clayey in South. 

 Norfolk, Cambridgeshire, Suffolk, and Essex, where Kimeridge Clay 

 and London Clay have been incorporated with other materials in 

 the Boulder-clay. In Huntingdonshire the Oxford Clay, and in 

 Northamptonshire the Lias Clay, have contributed to the Drift 

 a marked amount of debris. A local character has likewise been 

 imparted by the harder outcropping strata over which the Boulder- 

 clay has been distributed. 



Along the Midland branch-railway between Bourn and Saxby, 

 very fine cuttings of Chalky Boulder-clay were opened up. The 

 country was trenched in an east-and-west direction from the Oxford 

 Clay of Bourn to the Lower Lias near Melton Mowbray. Amongst 

 the Jurassic materials in the Boulder-clay there was a noteworthy 

 pi'eponderance of Oxfordian fossils in the eastern, of Gi'eat Oolite 

 fossils in the central, and of Lias fossils in the westei'n portion 

 of the area.^ 



Cuttings along the new London extension of the Manchester, 

 Sheffield, and Lincolnshire Eailway (now termed the Great Central 



1 Geol. Mag. 1897, p. 321 : abridgment of article on Englacial Drift in j 

 Technology Quarterly, vol. ix, Boston. 

 * H. B. W., " Jurassic Eocks of Britain," vol. iv, p. 422. 



