AND THE PHOSPHATIC BEDS NEAR ilONS. 



331 



The beds of cV have altogether a thickness of from 40 to 50 feet, 

 but the proportion of phosphate of lime diminishes with the depth. 

 Near the base the beds are almost entirely composed of carbonate 

 of lime, alternating with phosphatic layers. We pass thus without 

 sudden transition to the Chalk of Spiennes. 



E. Coarse Chalh of Sjnennes. — This is a coarse whitish chalk, 

 rough to the touch, forming regular beds, and composed almost 

 entirely of carbonate of lime. In it grey flint occurs abundantly, 

 both in isolated nodules and in continuous and massive layers. 



Fossils are somewhat rare in the Chalk of Spiennes. The prin- 

 cipal are : — 



Belemnitella mucronata, SckL, sp. 

 Ostrea vesicularis, Lanik. 

 Terebratula camea, 8ow. 



Rhyuclionella octoplicata, Sow., sp. 

 Echinocorys vulgaris, Breyn., var. ovata. 



These are the species found everywhere in the Upper White Chalk 

 of England, Germany, and France (Chalk of Meudon). They are 

 found also in the White Chalk of Nouvelles which uuderhes the Chalk 

 of Spiennes ; but in the latter, species appear which are only found 

 in the Upper Cretaceous deposits. These are : — 



Baculites Faujasi, Lamk. 

 Pecten pulchellus, Nils. 

 Lima semisulcata, Goldf. 

 Avicula caerulescens, Nils. 

 Ostrea acutirostris, Nils. 

 Rhynchonella subplicata, cV Orb. 



Terebratula Sowerbyi, Hagenow. 

 Trigonosemus PaHssi, Woodw. 

 Thecidea papillata, Bronn. 

 Crania egnabergensis, Eetzius, 

 Oardiaster aiianchvtis. d' Orb. 



The greatest ascertained thickness of the Chalk of Spiennes 

 exceeds 160 feet. 



I am of opinion that the Brown Phosphatic Chalk of Ciply (D) 

 and the Chalk of Spiennes (E) should be regarded as forming 

 together one geological whole, a peculiar stage of the Belgian 

 Cretaceous Series. This stage is here clearly defined by two 

 surfaces of denudation. Before the deposition of the Chalk of 

 Spiennes, the Chalk of jSTouvelles had been deeply eroded by denuda- 

 tion. The same was the case with the Brown Phosphatic Chalk 

 before the deposition of the Tufaceous Chalk of Ciply, but the two 

 surfaces of denudation are not parallel. Hence it results that the 

 superposition of the beds seen at Ciply and atMesvin, as represented 

 in fig. 2, does not exist everywhere on the line of outcrop of 

 the phosphatic beds. It is only in the workings at Mesvin that 

 the upper beds d} have been found. To the east of this locality 

 the Tufaceous Chalk (Tufeau) lies upon the subdivision d- or on d^. 

 Westward the two surfaces of denudation come near to each other, 

 near enough to account for the disappearance of the Chalk of 

 Spiennes, of all or a great part of the beds d\ and of all the beds cZ\ 

 In this last instance the superposition is indicated by fig. 3. 



