342 Prof. Sedgwick on the [May, 



Had we possessed no information respecting the beds imme- 

 diately above the chalk, except that which is derived from the 

 Isle of Wight, no one would, perhaps, have thought it necessary 

 to separate them into two fonnatioKS. So much may safely be 

 conceded to the objections we have been considering. We 

 must at the same time remark, that the section in Alum Bay 

 can hardly convey any correct notion respecting the classifica- 

 tion of the component beds, because the regular order of depo- 

 sition has been interrupted by a catastrophe which hurled all the 

 strata into a position entirely different from that which they once 

 occupied. Under such circumstances, it would be most unphi- 

 losophical to hasten to a general conclusion before other locali- 

 ties have been examined, in which the successive deposits have 

 met with no interruption, and in which all the accompanying 

 phenomena are exhibited in more perfect order. The Hampshire 

 coast from Studland Bay to the eastern termination of Hordwell 

 cliff, offers the best possible commentary on the formations of 

 Alum Bay ; for in that part of the basin, the lower beds have not* 

 been displaced since their first deposition, and are laid bare by a 

 succession of good sections. The sand and plastic clay forma- 

 ,tion occupies every portion of the cliff between Studland Bay 

 and Christ Church Head. In following the coast in that direc- 

 tion, the beds are found to have a slight inclination in a direction 

 about ESE. At the termination of the cliff of diluvium on the 

 cast side of the Christ Church river, these beds reappear with 

 the same inclination which gradually carries them under the 

 Lotidon clay. The line of demarcation is perfectly well defined, 

 and the London clay then occupies the whole cliffy and exhibits 

 a succession of beds of very great thickness. By the continued 

 inclination towards the imaginary centre of the basin, they are 

 successively brought down to the beach, and at length disappear 

 (nearly opposite the village of Barton) under formations, which 

 are evidently contemporaneous with the horizontal beds of 

 Headen Hill, and will be mentioned in their proper place. 



The portion of the sa?id and plastic clay formation, south of 

 Poole harbour, may be examined in any of the great pits which 

 have been opened in it. The following section, taken from one 

 of the clay-pits to the north-west of Corfe Castle, may serve as 

 an example. The beds are counted from the top. 



(1.) Yellow sand with ferruginous concretions. . . 20 or 30 feet. 

 (2.) A thin bed of ferruginous grit resting on impure 



wood coal 2 



(3.) Fine potter's clay 8 



(4.) Ferruginous grit, and very impure pyritous wood- 

 coal 2 



(5.) Good clay 5 



(6.) Dark impure clay 3 



(7.) Fine potter's clay 8 



(8.) Impure sand and clay of unknown thickness. 



