PRESTWICH BRITISH AND FOREIGN TERTIARIES. 235 



the London district is the greater importance of subordinate, very 

 fine, laminated clays. The fossils also, which in the Paris district 

 number 347, and which at Cassel have diminished to 18, are, with 

 the exception of a few vegetable remains, entirely wanting in the 

 London area. As, however, these are progressive changes, which 

 harmonize perfectly well in all their parts, they rather strengthen 

 than invalidate our position, for the dependence of all the collateral 

 phaenomena indicates a common origin, subject only to minor local 

 superadditions. It is only in proportion as the amount of carbonate 

 of lime in the sands diminishes and quartzose sands predominate, that 

 the number of Mollusks decreases. In French Flanders we have 

 intermediate palseontological and mineral conditions corresponding 

 with the intermediate geographical position. 



In this country 1 have traced the Lower Bagshot Sands as far east- 

 ward as the hills near Southend, in Essex ; they also apparently exist 

 in the Isle of Sheppey ; this carries them about 60 miles from Bag- 

 shot and to within 100 miles of Cassel (see Sect. 1 . PI. VIII). These 

 sands exhibit the same non-fossiliferous character in those districts 

 as around Bagshot, but they are of no great thickness, and the upper 

 portion, or that which is more fossiliferous in the Continent, is wanting. 



Following the " Lower Bagshots " further westward, and again 

 south-westward into Hampshire, they maintain nearly the same 

 thickness and mineral characters. They are, I think, represented in 

 White Cliff Bay by the Stratum No. 5 (" Section," Journ. Geol. Soc. 

 vol. ii. pi. ix. p. 223), which overlies the London Clay, and consists 

 of siliceous, and in parts clayey, sands, striped various shades of 

 yellow, 98 feet thick. This mass may probably correspond with 

 the *' Sables divers," and possibly include the "Lits Coquilliers," 

 although I do not think it unlikely that these latter may rather be 

 represented by some portion of the overlying beds. In the Alum 

 Bay section, it would be difficult to say how much of the series should 

 be included in this division. I should commence with the bed 7, over- 

 lying the London Clay (3 to 6), and carry it probably up to No. 18 

 or 20 {loc. cit.). In that case, it would include the foliated clays of 

 Stratum 1 7 with their beautiful group of plant- impressions. In some 

 of these beds green sands again occur as a subordinate character. 



At the base of the " Glauconie grossiere" according to M. Graves, 

 or at the top of the Sables Inferieurs according to M. d'Archiac, 

 is a very variable bed of foliated clay with occasional lignite. This 

 possibly may correspond with the lignite and foliated clay immediately 

 beneath the green sands of Bagshot, and with some of the carbo- 

 naceous clays and lignites above the sands last described in the Isle 

 of Wight. The Systeme Paniselien of M. Dumont may possibly 

 also be placed on this level. 



Not only, however, have we in the Bagshot district a series of 

 beds, which in mineral character, superposition, and importance corre- 

 spond in the main with the three upper divisions of the " Sables infe- 

 rieurs" of M. d'Archiac, but we further find them overlaid by other 

 beds corresponding with the '' Glauconie grossiere " or lower part of 

 the '' Calcaire grossier." Here again we must take into consideration. 



