284 Mr. Lyell on the Strata of the Plastic Clay Formation in the Cliffs 



These beds are about 25 feet in thickness. All these strata opposite Studland 

 are irregular and curved; and if the cUffs were more continuous, more verti- 

 cal and elevated, they would probably be seen to be contorted like the strata 

 of the same formation in White Cliff Bay, in the Isle of Wight. The section 

 between this and the chalk is very imperfect, the slanting cliifs being covered 

 with vegetation, pipe-clay (Pi. XXX. No. 1. o.) and white sand (PI. XXX. 

 No.l. n.) are seen at intervals. The junction of the chalk and sands is buried 

 under a mass of debris ; but fragments of a breccia of flint, imbedded in a ferru- 

 ginous cement, are observed immediately above the chalk. Mr. Mantell has 

 pointed out a similar breccia to me in the beds of plastic clay resting on the 

 chalk near Seaforth in Sussex, where the imbedded flint pebbles have a green 

 coating. I have observed these green pebbles in situ immediately over the 

 chalk in the North of Hampshire, and the green pebbles strewed over the chalk 

 near Croydon are probably derived from a bed similarly situated. 



Beneath the ferruginous breccia, the chalk for two feet is a soft marl, and 

 minutely striated with yellow and white lines, occasioned perhaps by stains 

 derived from the breccia. The upper chalk with flints then appears dipping 

 gently to the north. The Old Harry Rocks, which are detached masses of 

 chalk, standing out in the sea like the Needles in the Isle of Wight, are 

 not above half a mile distant fi'om this point. I found no animal remains in 

 any stratum between Christchurch Head and Studland Bay ; and although a 

 more careful investigation may detect some, they must certainly be rare. The 

 argillaceous strata of Alum Bay, which contain sheUs, are probably concealed 

 here at some of the interruptions of the section. But the absence of 

 animal and the abundance of vegetable remains are characteristic, both 

 here and on the continent, of the plastic clay or lignite-formation. They 

 are no less characteristic of the ancient coal-formation ; and it is also singular, 

 with respect to these two formations of dates so widely different, that the 

 proofs of their origin, whether freshwater or marine, have been considered 

 equivocal. In the ancient coal-formation, as is weU known, remains decidedly 

 marine have been found, but never abundantly nor in all coal-fields, while 

 sheUs of apparently freshwater genera have been often found. In France the 

 plastic clay-formation is usually destitute of organic remains ; but as lymnaBEB 

 and planorbes have been discovered in some localities, it is there generally 

 considered as a freshwater formation. The shells of the plastic clay of this 

 country are decidedly marine. Yet none who have compared the beds of 

 plastic clay and lignite resting on the chalk, in Prance, can doubt their ana- 

 logy to our own. Neither do such variances oppose any irreconcileable difficul- 

 ties to the connection of these formations ; nor are the variations in the fresh- 



