Page:VCH Bedfordshire 1.djvu/62

 A HISTORY OF BEDFORDSHIRE ture of the clays is of great benefit to agriculture owing to the amount of chalk which the boulder clay contains. While this clay occurs in such cases only as a thin sheet, some- times it attains a great thickness. Over a considerable area it is from 30 to 50 feet thick ; in the valley of the Ivel near Sandy, as already stated, it is known to attain a thickness of 104 feet, and in the same valley near Biggleswade it has recently been ascertained to be 90 feet in depth. In each of these localities it has been cut through in well- sinking, and in the latter a transported mass of Ampthill Clay, 67 feet in thickness, was found in its midst. 1 At the well at Northill near Sandy, which is west of the Ivel, the surface-level is about 105 feet above ordnance datum, and the base of the boulder clay which rests on Oxford Clay is therefore nearly at mean sea-level, while at the well near Biggleswade the surface-level is 160 feet above ordnance datum, and the base of the boulder clay which rests on disturbed and denuded Gault is 55 feet above mean sea-level. There is evidently a Glacial or pre-Glacial valley here which has been filled up by boulder clay, and it would be of great interest if its further extension could be traced. Biggleswade is on its eastern flank ; Northill may or may not be in its centre, but cannot be far off it ; and the evidence points to the conclusion that the Ivel flows through a valley of earlier formation than that of the Ouse above the junction of the two rivers ; but whether this valley, now nearly filled up by boulder clay, was the deep channel of a glacier or that of a powerful river which flowed in Pliocene times, if so probably during the period of greatest elevation of the land, can- not be determined without much further knowledge of the contour of the old land-surface beneath the boulder clay than we now possess. The boulder clay is a tenacious brownish or bluish clay con- taining numerous subangular fragments of rocks of various kinds, and sometimes large boulders, transported from a distance, with lumps of hard chalk and Liassic and Oolitic fossils, usually water-worn. Its boulders are ice-scratched, and glacial stria? may even be seen on its chalk pebbles. These are usually of hard chalk, red as well as white, very similar to that of the Yorkshire Wolds. The harder rock-fragments are of granite, syenite, quartzite, limestone, etc., from a distant source, and flints from the Chalk ; and the 'boulders,' as shown above, some- times take the form of huge masses of adjacent strata of a soft nature. Chalk in the boulder clay has even been quarried. At Toddington, a village situated nearly at the top of a hill which rises to a little over 500 feet above sea-level, there is a bed of gravel the precise geological age of which is uncertain. It has been described by Mr. Worthington Smith 3 from information given to him by the late Major W. C. Cooper of Toddington Manor. It is a flint-gravel with many 1 An account of this discovery was given by Mr. Henry Home in a paper read before the Geo- logical Society on 24 June 1903, and published since this was in type (l^jiort. Journ. Geo!. Soc. lix. 375-80- - In Man, the Primeval Savage, p. 69. 26