PRESTWICH WOOLWICH AND READING SERIES, 81 



The entire space between the London clay and the Chalk in the 

 Isle of Wight, varying from 90 to 140 feet, is occupied by this mass 

 of clay, with the exception of an irregular bed of 2 to 4 feet of sand 

 above and as much below it * ; the Basement-bed of the London 

 clay existing here in a mere rudimentary state, while the Thanet 

 Sands are wanting. This locality presents, in fact, the peculiar 

 mottled argillaceous structure of the Reading series in its greatest and 

 most exclusive development, being in fact almost as compact and im- 

 permeable as the London clay itself f. 



Proceeding from this centre either westward or eastward, consider- 

 able changes take place in these strata. In the former direction we 

 pass from the Isle of Wight over to Studland Bay J, where mottled 

 clays of a rather light colour appear to succeed to the chalk, but the 

 section is too obscure to determine the exact dimensions and super- 

 position of the beds : they seem to be thinner and more sandy. Be- 

 tween this point and Lulworth Castle I am not aware that any sec- 

 tions of these beds are exposed §. At Lulworth there is a small 

 section in the Park of light mottled red clays and some pebble beds 

 overlying the chalk. 



Proceeding toward Dorchester, the mattled red clays almost 

 disappear, and are replaced by coarse sands, irregular pebble and 

 shingle beds, and whitish clays. Two miles from this town towards 

 Wareham, the road cuttings on the hill show the chalk capped by a 

 few feet of tertiary beds, consisting first of brown ferruginous clay, 

 with light brown-coated unrolled flints, covered by a bed of small 

 pebbles, succeeded by brown clay, coarse sand, another fine conglo- 

 merate, and then mottled clay. The whole is not above 10 to 12 feet 

 thick, and fills up a very irregular and deeply indented surface of the 

 chalk II . About a mile further, near Little Maine, the chalk is over- 

 laid by sands, which in one place are concreted into large blocks of 

 sandstone, — the ordinary Druid sandstone. In a field adjoining the 

 road there is a complete nest of them, fifteen to twenty in number, 

 and varying in size from 2 to 6 feet in diameter. Westward of this 

 locality there are several outliers of these lowest tertiary beds, which 

 continue to show an increasing conglomerate character, the sands 

 becoming coarser and the clays whiter and mixed with pebbles and 



* Quart, Joum. Geol. Soc, vol. ii. pp, 255 & 259, and PI. IX, strat, " b," 



t In sinking one Artesian well at Portsmouth, a water-bearing sand bed was 

 met with in this series ; whereas in another well sunk at a short distance from 

 the first, the entire space between the London clay and the Chalk was occupied 

 with a solid and compact mass of mottled clays without a seam of sand, and con- 

 sequently without water, 



X For particulars of this section, and various points connected with the ter- 

 tiary geology of this district, see a paper by the Rev. W. B, Clarke in the Mag. 

 Nat. Hist, new ser. vol. iii. p. 390. 



§ The clays near Corfe are, I believe, higher in the series, and belong to the 

 Bagshot Sands. They are brought by the disturbances affecting that district into 

 close proximity to the Chalk. 



II This section is, however, rather problematical. The conglomerate contains 

 pebbles apparently of the palaeozoic rocks. The whole district requires a closer 

 examination. For a description of some Tertiary outliers to the west of Dorchester 

 see Dr. Buckland and Sir H. De la Beche, in Trans. Geol. Soc. 2nd Ser. vol. iv, p. 4. 



VOL. X, PART I. G 



