AND OF THE NEIGHBOURHOOD OF WATFORD. 101 



to the nature of its fossil contents. The lowest beds of this clay 

 are those which are exposed in the neighbourhood of Watford. 



Eeferring to the sections south of the Bushey Station (Fig. 5), 

 the brick-kilns at Watford Heath and Bushey, and near Hertford, 

 at Woodcock Hill, and at Hatfield Park kiln, we shall find, 

 overlying the Woolwich beds, layers of pebbles, sands, and loam, 

 with some marine remains, forming the base of the London Clay 

 proper. It is these which Mr. Prestwich calls the " Basement 

 Bed." See Pigs. 1, 2, 3, 4. 



There are traces of the London Clay in Hertfordshire, but it is 

 of no great thickness — in the northern district it is almost 

 wanting,* — but it attains the thickness of four or five hundred 

 feet in some parts of the London Basin, and consists of a 

 brownish or bluish clay, quietly but successively deposited in 

 a comparatively deep sea, and that sea to some extent open to the 

 north. The fossil forms are of a tropical character ; yet there 

 are indications also of a moderately temperate condition, and this 

 thick deposit of the London Clay, forming one of the chief features 

 of the London Basin, shows us therefore that it was accumulated 

 in a tolerably deep sea, with adjacent land, as is evident from the 

 plant and mammalian remains found in it. 



This Clay is not restricted to the present London Basin area. 

 It occurs in the Hampshire Basin ; but, singularly enough, the sea 

 does not appear to have covered any considerable portion of the 

 Paris Basin. There are traces of it in the neighbourhood of 

 Dieppe and Dunkirk, but considerably more is spread over a por- 

 tion of Belgium, where it is known as the Systeme Tpresien. 

 Possibly, says Mr. Prestwich, the London Clay may have been 

 formed during a period unrepresented, or only very partially re- 

 presented, in the French series. 



When we consider the nature of the Fauna and Flora — the 

 animal and vegetable life which existed at the time — we shall find 

 a very instructive lesson. There are, so far as at present known, 

 between four and five hundred species of animal remains. These 

 belong to nearly all the divisions of the animal kingdom, — 

 the largest number being the MoUusca, of which there are be- 

 tween 200 and 250 species. But all the other departments are 



drift and in part from thin cappings of the lower Tertiary beds, the hitter being 

 especially frequent to the north and north-west of Reading, and again around 

 Beaconsfield, Penn, and Amersham. They are also found to some extent near 

 St. Albans, Welwyn, and to the north of Hertford, and between Ware and 

 Bishop's Stortford." — Prestwich, ' Quart. Journ. Geol. Soc.,' vol. x. p. 19.— " In 

 the north-western corner of our district, in Bucks and Herts, there is absolutely 

 no downland, and the greater part of the tract consists of ploughed land diversi- 

 fied by woods and parks." — Whitaker, ' Guide to the Geology of London,' p. 21. 

 * " The London Clay forms the greater part of the London Tertiary district, 

 stretching eastward from the neighbourhood of Hungerford to that of Canter- 

 bury on the south, and to that of Bishop's Stortford on the north, and having 

 a breadth therefore of twenty miles and more at London : on the west, how- 

 ever, where the succeeding series is in force and the dip high, and as the 

 formation gets thinner, the outcrop is comparatively narrow, less than a mile 

 wide sometimes." — Whitaker, ' Mem. Geol. Survey,' vol. iv. 1872, p. 9. 



