GEOLOGICAL MUTATIONS. 159 



a stratum of reddish brown and mottled clay, 

 with seams of lignite ; and on this i.s superimposed 

 whitish sand and marl, with interstratiiied layers 

 of concretionary limestone, full of freshwater 

 shells. A thick bed of gravel forms the alluvial 

 covering on the summit of the hill. 



Geological ^mutations. — From this sketch of 

 the lithological characters and organic remains of 

 the strata in this locality, it will be seen that the 

 phenomena under review present a close analogy 

 to those observable in Whitecliff Bay ; the dis- 

 crepancy being inconsiderable, and such as may 

 have resulted from slight changes in the hydro- 

 graphical condition of the district during the accu- 

 mulation of the deposits. In both places there 

 are proofs that the commencement of the eocene 

 formation took place in a wide and open sea; the 

 first accumulation of detritus on the water-worn 

 surface of the chalk, being an argillaceous sedi- 

 ment, in which no animal remains were imbedded. 

 The earliest group of fossils, the Bognor series, 

 comprises the shells of marine mollusks that do 

 not inhabit deep sea-water, but live in depths 

 averaging from ten to twenty fathoms. This 

 depth, as Mr. Prestwich observes, would be ob- 

 viously inadequate to allow of the accumulation 

 of detritus sufficient to form strata, which, when 



