412 CRETACEOUS. 



other organic remains may be partly encrusted, or wholly enveloped by phosphatic 

 matter, while in some ' Coprolites ' the original organic structure has been obHter- 

 ated.' Between Hitchin and Camljridge the 'Coprolite' beds have been largely 

 worked. There are coprolite-diggings at Horningsea, Guilden Morden in Cam- 

 bridgeshire, Ashwell in Hertfordshire, and Shillington in Bedfordshire. The 

 phosphatic nodules are extracted by washing. The average yield is about 300 

 tons per acre ; and the nodules are worth about fifty shillings a ton. The diggers 

 usually pay about ;!^I40 an acre for the privilege of digging, and return the land at 

 the end of two years properly levelled and re-soiled. - 



The Totternhoe Stone (see also p. 404) is well shown in the large Chalk 

 quarries at Reach, and Burwell (Burwell Stone) in Cambridgeshire.''' At Reach 

 the Chalk Marl (clunch) has been most extensively worked, and the Totternhoe 

 Stone is only exposed at the western end of the quarry. It appears as a very 

 irregular dark-grey sandy limestone, about ten feet in thickness, containing towards 

 its base hard, brown and green, calcareo-phosphatic nodules ; the Chalk Marl 

 below is a hard, white, flaggy chalk. The Totternhoe Stone weathers into 

 numerous flaggy courses ; but if got out in masses and dried carefully (the blocks 

 being covered with matting to check the effects of the weather), the stone is useful 

 for building. It is also used for hearthstone. The Cherry Hinton Chalk of 

 Cherry Hinton, east of Cambridge, overlies the Totternhoe Stone, above 

 which comes the Melbourn Rock. (See p. 404.) These beds and higher strata 

 form the escarpment of Gog Magog and the Royston Downs. The beds above 

 the Melbourn Rock are grouped as Vandlebury Beds by Mr. Jukes-Browne, 

 from Vandlebury on the Gog Magog Hills, south-east of Cambridge.* (See Fig. 68.) 



BUCKINGHAMSHIRE, ETC. 



The Chalk forms the Chiltern Hills in Oxfordshire and Bucking- 

 hamshire, and the main divisions in this area (see p. 403) have 

 been noted by IMr. Whitaker.* In Bedfordshire the Totternhoe 

 Stone occurs at Totternhoe, Ivinghoe, Barton Hill, and 

 Kensworth Hill ; hills which form part of the Dunstable Downs, 

 and Avhich rise to a height of 810 feet at Kensworth Hill. The 

 stone is largely quarried for building-purposes, and it constitutes 

 a water-bearing stratum. (See p. 404.) At Luton the Chalk forms 

 the Luton Downs, and in this neighbourhood many fossils have 

 been obtained by Mr. J. Saunders.^ The INIelbourn Rock is 

 shown at Leagrave, north-west of Luton, and near Ravensburgh 

 Castle. 



In Hertfordshire the Chalk occurs near Hitchin, Hertford and 

 Ware, Northaw, Watford (see Fig. 72), and other places ; the 

 Chalk Rock is exposed at Boxmoor, near Hemel Hempstead,' and 

 the Totternhoe Stone is shown at Arlesey. 



In Essex we find the Chalk exposed at Great and Little Chester- 



^ O. Fisher, Q. J. xxviii. 396 ; see also W. J. Sollas, Q. J. xxviii. 397, xxix. 

 63, 76. 



- Fisher, Q. J. xxix. 52. 



^ See Rev. J. Hailstone, T. G. S. ii. 248 ; Penning and Jukes-Browne, Geol. 

 Cambridge, p. 43. 



* G. Mag. 1S80, p. 257 ; Q. J. xxxi. 272, and Geol. Cambridge, p. 24 ; see also 

 W. Hill and A. J. Jukes-Browne, Q. J. xlii. 216. 



^ Q. J. xxi. 398 ; see also W. Hill and A. J. Jukes-Browne, Q. J. xlii. 216. 



I G. Mag. 1867, pp. 157, 543. 



' Whitaker, Geol. Middlesex (Geol. Survey), etc. p. 7. 



