210 



of the Kentish quarries, which is the chief point of contrast hetween 

 the sections there and in Kent, is deserving of great attention. The 

 rag, though very unequally distributed (as is not unusual with beds 

 which have so much of a concretional character), extends without 

 material interruption from the Kentish coast to the neighbourhood 

 of Godstone ; its greatest expansion being at Maidstone, where the 

 thickness exceeds 1 20 feet ; Avhile Mr. Simms's section proves that 

 the Hythe quarries are nearly of equal thickness. The decrease, 

 therefore, in the proportion of calcareous matter, in receding from 

 what may be called this central region of the limestone, — either 

 inland, through Surrey and Hampshire, or westward, by the coast 

 of Sussex to the Isle of Wight and Dorsetshire, is very rapid ; and 

 is the more deserving of notice in the Isle of Wight, as the total 

 thickness of the lower greensand (both near Shanklin, on the east, 

 and westward from Blackgang Chine to Atherfield), cannot be less 

 than 400 feet,' — the thickness of the groups below the gault at Hythe, 

 according to Mr. Simms. 



This reduction of the calcareous matter between Maidstone and 

 Surrey is the more remarkable, as the sands throughout that in- 

 terval are absolutely continuous : the distance from Maidstone to 

 Redhills, where there is no appearance of limestone, being only 30 

 miles ; that between the central limestone at Hythe and Atherlield 

 being about 115 miles. The equivalent of these calcareous beds 

 must be sought for in Surrey and Hampshire, in those ranges of 

 concretional stone which are there distributed irregularly, but in a 

 somewhat stratigraphical arrangement, through the lower green- 

 sand ; as in the " Bargate stone ; " the chert of Leith Hill, &c. ; and 

 generally, the sands of all that region ought to be examined atten- 

 tively, with a view to their comparison with the cliffs between Black- 

 gang Chine and Atherfield. 



§. The separation of the lower greensand from the other subcre- 

 taceous groups, was founded on its obvious stratigraphical distinc- 

 tion, from the Gault on the one hand, and from the subjacent Weal- 

 den on the other : and the subdivisions were derived, from the pro- 

 minence of certain natural features of the surface, evidently corres- 

 ponding to the composition and succession of the strata. The ex- 

 pediency of these subdivisions in the coast section at Hythe appears 

 to be confirmed by Mr. Simms's survey ; his section, when reduced 

 to the natural scale of height and distance, showing that the features 

 of the country agree with the division of the strata between the 

 gault and the bottom of the calcareous beds into three groups : and 

 II the clay newly discovered beneath the quarries be added to the 

 series, it will form another subdivision, accordant with the principle 

 of arrangement above mentioned. The chief question remaining 

 with respect to this lowest group of marine clay is, whether it will 

 be necessary to detach it altogether from the other divisions of the 

 lower greensand ; and this cannot be decided without a deliberate 

 review of the subcretaceous fossils, — and of the strata which afford 

 them. 



