DEPOSITS OF nERTFOEDSHIRE. 



105 



These deposits are exposed and may be examined in nearly all 

 the valleys south of the chalk escarpment. They may be seen 

 in the railway-cntting north of Hatfield, and in a pit on the 

 hill-side east of Horns Mill. They can be traced all alonj? the 

 hill-side from that place to Hatfield, near Colo Green Station, 

 and south of the Mimram near Tewin. In the road-cutting south 

 of Broad Oak End Farm, and along the west side of the Beane 

 between that place and Hertford, some boulder-clay, with glaciated 

 stones, occurs at the base of the gravels. In the gravel-pits near 

 Ware, some finely laminated brick-earth, belonging to the Mid- 

 glacial series, is seen to be folded and crumpled up and then 

 covered by horizontal beds in the way usually ascribed to ice- 

 action. At Camp's Hill there is also a brick-earth in the Mid- 

 glacial beds, beneath which bones of reindeer, mammoth, and 

 rhinoceros have been foimd.* Mr. S. V. Wood found at Stevenage, 

 in the brick-earths intercalated in the Middle Glacial formation, 

 several specimens of Odrea edulis, a non-arctic shell, f Messrs. 

 Wood and Harmer have obtained 26 species of MoUusca from this 

 middle division in other parts; but I know of only this one in- 

 stance of fossils being found in the !Mid-glacial of our county. 

 Some of the clays in the midst of the gravels prevent the passage 

 of surf ace- ^vater to the gravels beneath, which therefore keep their 

 grey colour, the top gravels being stained red. 



Fig. 3. — Section showing the Boulder-clay on the top of the 



Chalk Escarpment. 



klffAH 



tOTSTON RCtD GRESM 



I i 



BUSTlNoroRB 



HON DEN 



X. Post-glacial. T. Upper Glacial (Boulder-clay). E. Mid-glacial. C. Chalk.J 



P. Gault. 



Upper Glacial. — As will be seen from the sections, there is, over- 

 lying the beds previously described, the Boulder-clay, which is a 

 clayey deposit full of pellets or pebbles of chalk, containing also 

 chalk-flints and blocks of various rocks, transported from distant 

 localities and scratched and grooved by ice-action. Fossils, where 

 found, are derived chiefly from the Lias and Oxford Clay. This 

 deposit formed one continuous sheet through which the present 

 valleys have been cut in post-glacial times. It spreads alike over 



* ' Quart. Joum. Gaol. Soc.,' vol. xxiv, p. 287. 



t /*. p. 468, and Woodward's ' Geology of England and Wiles,' p. 312. 

 X The Chalk here is nearly horizontal, not vertical as might be inferred from 

 the section. — Ed. 



