304 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [May 19, 



also laboured successfully in distinguishing the fossils of the several 

 strata, observing which are peculiar to each, and which of them com- 

 mon to different members of the series, so that after I had visited the 

 principal localities in his company, I was able to make myself master 

 of a great body of information which it would have required years of 

 unassisted labour to acquire. In tracing the subdivisions of the 

 strata from one locality to another, and in identifying them in different 

 places by aid of mineral character, we had the advantage of having 

 been preceded by M. Dumont, whose patient and conscientious 

 labours in constructing the map of Belgium cannot be too highly 

 estimated. The task of unravelling the geological relations and geo- 

 graphical limits of the several groups in such a region is attended 

 with no ordinary difficulties, in consequence of the frequent dearth of 

 organic remains, and on account of a deep and almost continuous 

 covering of loess. The resemblance to the older strata, moreover, 

 of some deposits of loess, formed at the expense of denuded tertiary 

 beds and containing the same fossils, adds greatly to the confusion. 



After visiting Bergh, Vieux Jonc, Hoesselt, and Lethen near Kleyn 

 Spawen (see Map, PL XVII. fig. 4), and the villages of Neerepen 

 and Grimittingen, places familiar to the student of Nyst's work on 

 the fossil shells of Belgium, and after considering the data liberally 

 supplied to me by M. Bosquet, I thought it most useful, at least as 

 a provisional classification, to divide the Limburg tertiaries into 

 Upper, Middle, and Lower (D 1, D 2, and D3, Table I. p. 279), the 

 first and last being marine, and the middle a fluvio -marine deposit. 



Table VIII. 

 Limhurg Beds near Kleyn Spawen. 



Thickness. 



TT / • \ f Nucula-loam (" couche argilo-sableuse a Nu- "1 „ f^^+ 



Upper (marine)... I eules," Bosquet) \ ^ ^''*- 



T>, .J. . f a. Berarh sands 14 ,, 



Middle (fluvio- I ^ yeUowish sands 6 „ 



™^"^^^) [e. Green marls 36 „ 



, , • \ \ Glauconiferous sandy clay, or Ostrea ventila- \ ^a 



LowER(marme)...| ^^^^ ^ed | ^^ " 



The uppermost bed of the above Table, called " the Nucula loam," 

 at Bergh is a mixture of sand and clay, in which the twenty-one species 

 of Mollusca and eleven species of Entomostraca, enumerated in the 

 second column of asterisks in Table IX. p. 312, occur. The Nucula 

 Lyelliana, Bosq., is the most common shell of this bed, though diffi- 

 cult to obtain entire, owing to its fragile condition. All the other 

 shells are rare except the Corbulomya complanatay which is the only 

 one of the whole not decidedly marine. Next to Nucula Lyelliana 

 the Cytheridea MuUeri, Bosq., is the commonest fossil. In regard 

 to the probable depth of the sea. Prof. E. Forbes supposes it to indi- 

 cate the lower part of his perilittoral zone. 



Of the twenty-one species of Mollusca the following twelve species 

 are common to this bed and to the clay of Rupelmonde, Boom, &c.. 



