Vol. 52.] EOCENE DEPOSITS OF DORSET. 491 



type. At Lancing the strata are mainly of the Reading type, 

 consisting of alternations of red-mottled clay, loam, lignite, and sand ; 

 but even there certain ironstone-nodules near the base yield casts 

 of marine shells. Prom Worthing westward the southern margin 

 of the Hampshire Basin yields no evidence of marine conditions. 



An increasing rarity of marine fossils is not the only change that 

 takes place when the Woolwich and Heading Series is traced west- 

 ward, for directly we pass from Hampshire into Dorset it is notice- 

 able that the sands are often coarse and full of small splinters 

 of flint. A few miles farther west, at Morden and at East Lulworth, 

 lenticular masses of coarse subangular gravel make their appearance 

 in the Reading Beds, and these gravels, especially at Morden, contain 

 a considerable percentage of Greensand chert with sponge-spicules. 

 This admixture of coarse sand and subangular gravel becomes still 

 more marked towards the western limits of the formation, and the 

 proportion of Greensand chert increases. 



2. London Clay. 



Though the London Clay thins and becomes more sandy to the 

 west, there is no sign of shore or estuarine conditions, and even at 

 its western limit it is apparently of purely marine origin. The 

 flint-pebbles at the base of the formation are all perfectly rounded, 

 as in other localities, and do not yield any evidence of beaches. The 

 only fossil that I have seen from the London Clay in Dorset is an 

 indeterminable bivalve, apparently a Cyprina or Cytherea, obtained 

 from the basement-bed in a boring at Wimborne. This absence of 

 fossils is, however, in all probability due to the sandy pervious 

 nature of the deposit; for though more typical London Clay with 

 septarian ironstone-nodules occurs, sections in unweathered material 

 are very scarce. Throughout the Hampshire Basin the London 

 Clay seems always to rest, with a sharp, slightly eroded junction, on 

 the Reading Series; yet there is no trace of either unconformity or 

 overlap, the thickness of the Reading Beds remaining approximately 

 the same throughout. 



3. Lower Bagshot Beds. 



The changes undergone by the Bagshot Sands are even more 

 marked than those that take place in the Lower Eocene strata. 

 It' we follow the southern margin of the Hampshire Basin we 

 discover that the Sands are thin and scarcely recognizable in the 

 Selsey Peninsula. In the Isle of Wight, however, they expand 

 enormously, reaching 150 feet at the eastern end of the island and 

 600 feet at the western, where they contain lenticular masses of white 

 pipe-clay with plant-remains. The Bournemouth cliffs show a 

 tendency to the increase of coarse sands, containing small fragments 

 of black grit, lydite (or radiolarian chert), and occasionally of 

 Greensand chert ; splinters of flint also begin to appear. Coarse 

 sands of this character continue to be associated with the pipe-clays 

 westward to beyond Wareham. Then sets in a change like that 



