4i8 



THE GEOLOGIST. 



tliis respect in the slightest degree, and the same exceptional cases 

 as rarely occur among the true crinoids. 



If we examine the echinoderms from the Oolite, the Chalk, or the 

 Tertiary beds, we find them one and all reclining on their broadest 

 diameters, in fact, obeying the laws of gravitation, but which appears 

 to have been overcome in Paleechinus by some countervailing 

 influence, which resisting force was probably an elongated column. 



It must be understood that I do not positively maintain that 

 Paleechinus was attached to the sea-bed by a jointed flexible column, 

 but that one evidence in favour of such an addition to its character 

 is strong, if not convincing. 



GEMS OF PRIVATE COLLECTIONS. 



UNIO Als^D PALUDIN^. 



From the Wealden Beds of Kent, in the collection of 

 Me. W. Haeris, E.G.S., of Charing. 



The Sussex Marble, or Bethersden Marble, as it is indifierently 

 termed according to its occurrence in Kent or Sussex, is found also 

 in Surrey, near the foot of Leith Hill. It occurs in thin courses of 

 variable thickness and extent, but seldom presenting a bed one foot 

 thick, in the weald clay. 



It is made up chiefly of the shells of Paludince, whole or in frag- 

 ments. Occasionally the shells retain their form, as in the specimen 

 figm'ed, and weather out on exposure ; but often only their casts are 

 exposed, the matrix being calcareous matter derived from the disinte- 

 gration of the shells. The shells of Uniones also occur ; rarely, as 

 in the specimen figured, retaining this form ; more often as casts. 

 Cypridte also occur in abundance ; but the small size of the tiny shells 

 or valves of these little entomostraca cause them to be overlooked. 

 The Ci/pridca VaJdcnsis is the common species. The animal matter 

 of the Paludino3 appears to be often preserved in this marble, and 

 gives to the polished sections the dark grey and black markings so 

 characteristic of the stone. Purbeck marble is a similar stone, older 

 than that of the weald cla}^, and formed of a Paludina of smaller size. 



The Paludina of the Sussex marble is scarcely to be distinguished 

 from that of the existing rivers and ponds, namely, the P. vhijjara ; 

 but Sowcrby points out that it has a thicker shell, and is somewhat 

 turbo-like in aspect ; and has termed it P. fluviorum, (Min. Conch., 

 pi. 31. fig. 1 ; vol. i, p. 77, and vol. vi. p. 192). A larger form from 



