Dr. FiTTON on the Strata below the Chalk. 215 



Portland. The structure in this case is, in fact, analogous to that of the 

 Isle of Wight ; except that the top of the curve has in that place been car- 

 ried away, and that what remains of the upper strata on the south of the 

 island is much less inclined. 



(109.) Coast west of Purheck. — The sections west of the Isle of Pur- 

 beck, as far as Whitenore on the coast of Dorsetshire, have been generally 

 described and represented by Mr. Webster with his usual clearness *, but 

 have not yet been examined in detail. The Purbeck strata especially are 

 disclosed there under a great variety of aspects, no fewer than nine sections 

 of the beds between the chalk and Portland stone being visible, on the shore 

 of the small bays by which the coast is indented, within the short space of five 

 miles f. One of the most remarkable circumstances in the structure of this 

 part of the coast, is the rapid convergence of the strata in proceeding west- 

 ward from the Isle of Wight; the total distance from the top of the green- 

 sand to the beginning of the Portland stone, which, between Ballard Downs 

 and Durlstone Head is about two miles and a half, being reduced to about 

 150 paces at Durdle Cove. The sectional sketches PI. X.a. Nos. 8. to 10', 

 which are drawn to the same scale, exhibit the proportion of this reduction ; 

 and Pl.X. b. figs. 7. and 8., show on a much larger scale, the detail of the beds 

 in the east side of Lulworth Cove, and on the east of the isthmus connecting 

 the ridge of Portland stone with the chalk, at Man-of-War and Durdle Coves; 

 beyond which some detached vertical masses, standing out in the sea like 

 walls, and successively coming nearer to the main cliff, are the last indica- 

 tions of the beds below the chalk upon this part of the coast. 



In these western sections of the groups immediately below the chalk it is impossible to recog- 

 nise all the subdivisions of the coast of Kent, and the adjoining counties ; the separation between 

 the upper and lower green-sands having in a great measure disappeared, and the latter being 

 greatly reduced in thickness, or wholly united with the upper sands. In the Wealden, likewise, 

 the clay can scarcely be separated from the strata representing the Hastings-sands, which occupy 

 a considerable space ; and here, as in the Isle of Wight, the proportion of red and variegated 

 sandy clay to the ferruginous sands is very great, one distinct group of such clay being observ- 



* Letters, &c., pp. 185-6, 193-7. 



t These sections are : 1. Worharrow Bay. 2, Mewp Cove, not named in the Ordnance Map. 

 3. Bacon Hall, a nook on the west of Mewp. 4. and 5. Lulworth Cove, east and west sides ; 

 PI. X. a. No. 1 0. ; and X. b. fig. 7. 6. Stare Cove. 7. West of Horse-walls. 8. Man-qf- War Cove ; 

 PI. X. a. No. 10'., and PI. X.b. fig. 8. 9. Durdle Cove. The coast hereabouts being difficult of 

 access, and the adjacent country thinly inhabited, I believe that the best stations for a geologist 

 who wishes to examine it with ease, would be Swanage, for the eastern part of the Isle of Purbeck ; 

 and East Lulworth, for the coast westward. A good boat should be taken in calm weather, at 

 Lulworth Cove or at Worbarrow, to view the cliffs from the sea. 

 VOL. IV. SECOND SERIES. 2 F 



