J. S. Gardner — Correlation of the Tertiary Series. 151 



The Head itself contains a separate sequence, the Hengistbury 

 Head beds. The uppermost layer is white sand with an orange 

 clay layer at the base. The main mass of the Head is composed of 

 brown clay, to which it owes its preservation. This stiff clay has 

 resisted denudation and the layers of ironstone which it contains, 

 falling into the sea, have formed a protecting barrier. 1 Below 

 the clay is a green sand bed, and lastly we find black, chocolate- 

 coloured, and white sands, belonging to the same Upper Marine 

 Series which we have seen capping the Boscombe Cliff. 



The highest beds, above alluded to, I have traced across to the 

 base of High Cliff, where they had already a place assigned to them 

 in the Bracklesham Series. 2 



The Bracklesham Beds. — It is difficult to distinguish these at 

 Alum Bay from the overlying Barton Series. Prof. Prestwich indeed 

 grouped both in one bed, No. 29, but Mr. Fisher 3 has shown that 

 the lower 43 feet form a portion of the Bracklesham Series. The 

 most complete section is at Whitecliff Bay, where almost every 

 bed that has been met with on the main land is represented. The 

 whole group consists of alternations of sand and sandy clay, the clays 

 being more prevalent in the highest member, the sands in the 

 lower. Green grains abound in all the beds. Many of the beds 

 are laminated, being formed of alternations of very thin bands of 

 clay, separated by sandy layers, and contain vegetable matter. The 

 best known localities, and those from whence celebrated collections 

 of fossils have been procured, are Bracklesham or Selsey, Stubbing- 

 ton, and near Bramshaw in the New Forest. At Highcliff, the 

 junction between the Bracklesham and Barton beds is placed by 

 Fisher at the Nummulina Prestioichiana bed, 35 feet above the white 

 Hengistbury Head Sand at the base of the cliff. As the Bracklesham 

 Series are at Whitecliff Bay 530 feet thick, we see that there is a 

 probability that the whole of the Marine Series of Bournemouth, 

 with the Hengistbury Head Beds, may be contemporary with them. 



The Middle and so-called Upper Bagshot Beds of the London 

 Basin. — The Middle Bagshots, representing the Bournemouth and 

 Bracklesham beds, have no great extension in the London Basin, 

 and do not exceed forty to sixty feet in thickness. They more resem- 

 ble the Bournemouth beds than the true Bracklesham series. Their 

 principal development is round Chertsey and Addlestone. They are 

 easily recognized by their sands and clays with green grains, which 

 also distinguish them from the Lower Bagshot beds. They seldom 

 contain fossils, but enough have been found to identify them with 

 Bracklesham. 



It appears to me that there is not the slightest reason to suppose 

 that any Upper Bagshot beds are present in the London Basin. The 

 absence of Barton clay, and the identical character of the beds with 

 the Upper Marine beds of Bournemouth, renders it unlikely that 



1 I have made frequent but unavailing search for the leaves marked on the Geol. 

 Survey Map as occurring here, but I have found leaves in the same beds in a 

 brick-pit inland. 

 2 Rev. 0. Fisher, Q. J. G. S., 1862, vol. xviii. p. 67. 3 Q. J. G.S., 1862, vol. xviii. p. 84. 



