1847.] PRESTWICH ON THE LONDON CLAY & BAGSHOT SANDS. 409 



In the sections of Alum and White-Cliff Bays the niunbers on the side refer to 

 the more detailed sections given in ray previous paper (see Journal Geol. Soc. for 

 Aug. 1846). As they are there given in full, only the fev? portions necessary for 

 the elucidation of the subject are repeated here. The colouring is omitted for the 

 same reason. 



The Barton chff section represents the strata as far as Muddiford near Christ- 

 church. The base of the Barton clays is there exposed reposing upon light- 

 coloured sands without fossil shells, but full of fragments of soft carbonized wood. 

 A break in the strata is then made by Christchurch harbour, on the other side 

 of which the cliffs resume and range uninterruptedly to Poole harbour and the 

 chalk at Studland. The strata, of coarse sands and impure clays, forming these 

 cliffs correspond with the central beds of Alum Bay and the Bracklesham Bay 

 series. No fossils have been found in them except the vegetable impressions 

 at Bournemoutb. For a description of these strata see Mr. Lyell's memoir (Trans. 

 Geol. Soc, 2iid Series, vol. ii. p. 279). 



The colouring of the sections indicates roughly the most generally pi'evailing 

 colours of the several formations. 



Section 1 shows the superposition and range of the strata composing the Hamp- 

 shire system, and the relative position of the strata of Barton, Bracklesham and 

 Bognor, from Bognor through Cowes to Christchurch. 



Section 2 exhibits the range of the tertiary strata from London to the Isle of 

 Wight; shows the slight curve by which the chalk is elevated, and the continuity 

 of the two tertiary districts interrupted. A few outliers of the lowest tertiary 

 beds (not marked here) occur at intervals on the range of chalk hills separating 

 the two districts. 



In both these sections (1 and 2) the horizontal and vertical measurements are 

 on the same scale*. The few faults that occur in these strata are omitted. Of the 

 two systems, that of Hampshire is by far the most disturbed. 



The Map shows the relative positions of the Hampshire and London systems. 

 The outline of the latter I can give as the result of my own observations : — that of 

 the former I have taken chiefly from Mr. Greenough's large map. 



* Owing to the minuteness of the divisions this scale has not been well kept in 

 the plate. The vertical proportions are in most parts of it in excess. 



In section 2, the strata reposing upon the London clay from near Odiham to 

 Claremont represent the three divisions of the Bagshot sands. The lower divi- 

 sion should have appeared again on the summit of Hampstead Hill, which is also 

 made to appear too high. 



CORRIGENDUM. 



In Table 2, page 400, reckon one more species in addition and common to 

 Barton and Bracklesham. 



