﻿"Vol. 64,] CHANNEL OF DEIFT AT HITCHIN. 21 



The coarse gravel contains a large quantity of Jurassic debris, 

 much of which occurs in rounded boulders, many as big as a man's 

 head. These are of soft material, and are picked out and cast aside 

 by the workmen. Up to the present the bottom of this gravel has 

 not been reached. 



At Mr. Theodore Ransom's lime-works at Hitchin Railway-station, 

 Boulder-Clay, from which ice-scratched blocks of limestone and 

 sandstone of very considerable size have been obtained, is seen 

 overlying the Chalk. At Gravelly Hill, near Great Wymondley, the 

 material consists of Jurassic debris, limestone, sandstone, quartz, 

 and quartzite-pebbles, etc. Several pits at the Folly, Hitchin, 

 expose gravels of similar nature. Overlying these, and covered by a 

 considerable thickness of brick-earth, is the old river-bed described 

 by Mr. C. Reid.' 



Recent excavations for building purposes have shown that 

 Boulder-Clay with ice-scratched stones occurs in patches all along 

 the highest parts of the Highbury Ridge. 



A gravel of different character occurs on Wilbury Hill. In an old 

 gravel-pit on the summit of the hill, a thickness of about 8 feet of it is 

 shown, overlain by about 7 feet of pale-brown calcareous loam. This 

 gravel consists almost entirely of smallish angular and subangular 

 flints and many well-rounded chalk-pebbles. Besides these, it con- 

 tains pebbles of quartz and quartzite, rolled fragments of a pinkish 

 or red rock (not red chalk), none of which exceed IJ inches in 

 length, and also many small pieces of ironstone. The Jurassic 

 debris seen in the pits near Hitchin, with fossiliferous limestones, 

 gryphaeas, and belemnites, is absent. About a third of a mile to 

 the north-east, the same gravel has been extensively dug by the 

 ' Garden City ' authorities, some of the sections showing 12 to 14 feet 

 of it. It is here much seamed by layers of quartz-sand containing 

 also a good deal of fine chalk: these layers show current-bedding. 

 Still farther on, the gravel seems to pass laterally into a sharp 

 quartz-sand with a few chalk-stones. The sand is closely associated 

 with Boulder-Clay, although the actual relation of the one to the 

 other has not yet been disclosed. There is good reason for believing, 

 however, that the sand and the gravel are overlain by the clay, for 

 the 3 or 4 feet of soil overlying the gravel contains large pebbles 

 of sandstone, limestone, etc. ; and in the pit where the sand is dug, 

 masses of Boulder-Clay full of large weathered and rounded frag- 

 ments of Melbourn Rock have been encountered near the surface. 

 It is curious that the outcrop of the Melbourn Rock occurs Avithin 

 200 or 300 yards. It seems probable that these gravels of Wilbury 

 Hill are older than any part of the Drift seen at Hitchin. 



Y. Summary, 



From the evidence adduced in the foregoing pages there seems 

 little reason to doubt that a channel of considerable depth, now 

 filled with J)rift, occupies the centre of an old valley in the Chalk- 



^ Proc. Roy. Soc. vol. lii (1807) p. 40 ; see also Proc. Geol. Assoc, vol. xiv 

 (1895-96) p. 415. 



