564 MESSES. JUKES-BROWNE AND W. HILL ON THE LOWER PAET 



Part of the above succession can be seen in the quarries at 

 Swaffham Bulbeck, west of Newmarket, but there are no good 

 exposures north of Newmarket. When the Bury and Soham rail- 

 way was being made, in 1879, Mr. Whi taker recognized the 

 Melbourn Bock and its underlying bands of shaly marl (zone of Bel, 

 plena) in one of the cuttings south-west of Snailwell ; and it is pro- 

 bable that the springs which rise below the church at Snailwell issue 

 from the Melbourn Bock. 



The outcrop of the Melbourn Bock is an important line to trace, 

 because it fixes the uppermost limit of the Lower Chalk and the 

 base of the Middle Chalk. It probably runs through Chippenham 

 Park, and then passes beneath the great spread of valley-gravel 

 which lies between Chippenham and Kennet ; north of Kennet the 

 country is covered by blown sand, but near Worhngton-Heath farm 

 there is a pit exposing the lower beds of the zone of* Bhyncli. Cuvieri 

 and what seems to be the topmost bed of the rock itself. The section 

 was as follows : — 



feet. 



Gravelly soil and rubble 4 



Hard, nodular, whitish rock in thin beds, full of 



Inoceramus mytiloide* and Rhynch. Cuvieri 4 



Thin seam of greenish-grey marl. 



Hard nodular rocky chalk, white with greenish 



matter between the lumps (no fossils) 3 



Talus hiding chalk below 4 



The beds appear to have a slight dip due east. 



The gravel which forms such an extensive tract between Presk- 

 enham and Worlington seems to be banked against the ridge formed 

 by the outcrop of the Melbourn Bock, and this will account for the 

 sudden emergence of the Chalk from beneath the gravel plain. The 

 rock is again seen in the cutting on the new railway to Mildenhall, 

 just south of Worlington House, and it appears to have been formerly 

 quarried by the side of the main road N.E. of that house. 



On the north side of the river we could not find any trace of it, 

 the large quarries at West Bow being opened in the grey chalk, 

 which here contains a remarkable band of reddish chalk ; the details 

 of this section have been given elsew T here *, and need not be repeated 

 here. 



Mildenhall itself stands on the hard, shelly, yellowish chalk of the 

 zone of ffliynclwnella Cuvieri, chalk of this description and containing 

 that fossil together with Inoceramus mytiloides and Echinoconus 

 subrotundus being exposed in a small pit at the east end of the 

 town. 



The chalk by the roadside, a mile and a quarter north-west of 

 Mildenhall, appears to be the white blocky chalk which forms the 

 upper portion of the zone of Holaster subglohosus, and the outcrop 

 of the Melbourn Bock must therefore sweep round the western and 

 northern sides of the town to the south end of the long inlet of fen- 

 land which runs by Eriswell. All the exposures which we could 



* .Brir.. Assoc. Bep. 1886, and Geol. Mag. dec. iii. vol. iv. p. 24. 



