A HISTORY OF HERTFORDSHIRE 



and arrangement, and contain many sub-angular flints and some un- 

 broken and almost unworn ones, with drifted Oolitic and Liassic fossils, 

 chiefly gryphasas and belemnites, and echinoderms and other fossils de- 

 rived from the Chalk. Much false-bedded sand also often occurs, and 

 sometimes a bed of loam or clay. ' These deposits are exposed and 

 may be examined in nearly all the valleys south of the Chalk escarp- 

 ment. They may be seen in the railway-cutting north of Hatfield, and 

 in a pit on the hill-side east of Horn's Mill. They can be traced all 

 along the hill-side from that place to Hatfield, near Cole 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 found. Mr. S. V. Wood found 

 at Stevenage, in the brick-earths intercalated in the Middle Glacial 

 series, several specimens of Ostrea edulis, a non-arctic shell . . . the 

 only instance of [contemporaneous] fossils being found in the Mid- 

 glacial of the county.' ' The Middle Glacial beds are thus seen to be 

 widely spread over the county, and to be very variable in their origin 

 as well as in their nature. 



Possibly the prevailing impression with regard to this period does 

 not quite accord with the facts, the term Interglacial which has been 

 applied to it being to some extent misleading. Although the only con- 

 temporaneous fossils known indicate a temperate climate, there are in- 

 dications that the seas of the period were not free from icebergs. The 

 (so-called) ' foreign rocks ' found in our Mid-glacial gravels, which must 

 have been carried a great distance from the north, being fragments of 

 much older rocks than occur in Hertfordshire, and the fossils derived 

 from distant formations, indicate some other transporting agent than 

 rivers or ocean-currents, while the presence of local patches of boulder- 

 clay with glaciated stones, confirms the view that ice-action was not 

 entirely absent. A temperate climate is not incompatible with the 

 occasional presence of icebergs drifting from the north ; but the more 

 likely explanation of the anomaly is that this period was one of long 

 duration, generally cold but with mild intervals when a temperate 

 molluscan fauna migrated to the seas of the British archipelago from 

 the warmer southern waters. Such milder intervals would be most 

 likely to occur when the depression of the land was greatest, and the 



1 Elsden, 'The Post-Tertiary Deposits of Hertfordshire,' Trans. Herts Nat. Hist. 

 Sac., vol. i. p. 105 (1881). Prestwich has recorded the finding of pieces of the tooth and 

 tusk of an elephant in gravel, which he believed to pass under the boulder-clay, at Bricket 

 Wood near Watford, but there is some doubt as to the position of this gravel. Geologist, vol. 

 i. p. 241 (1858). 



22 



