236 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [Jail. 24, 



of a geological period. In the case of the Bolderberg there was no 

 difficulty in identifying the upper ferruginous sands with those of 

 Diest, and overlying some older system, ending upwards in a shingle- 

 bed. 



So far as the " Systeme Bolderien" of M. Dumontis concerned, 

 its geological value is dependent on this simple consideration, — Is the 

 shingle-band connected with the sands below or the sands above ? 

 In nine cases out of 10 throughout the whole series of geological 

 formations the shingle, gravel, and conglomerate beds form the base 

 of each natural group of accumulations. In the case of the Bolder- 

 berg there is no ambiguity whatever, the break and unconformity, 

 whatever it may be worth, occurs below, and from this line there is 

 a progressive change upwards from sands with shingle to sands 

 without ; the whole mass of the upper ferruginous sands forming a 

 continuous series, and differing from the capping to the hills about 

 Louvain only in the circumstance of the fossils it contains. The 

 lowest bed represents a littoral line; the higher sandy beds, the 

 zone of drift-sand and of the Crag sea ; the whole having been ac- 

 cumulated slowly as the area was being depressed or submerged. 



Zoologically, the '^ Systeme Bolderien " has been represented as a 

 true Miocene formation of the age of the Faluns of Touraine*, and 

 this has constituted its palaeontological interest. Sir Charles Lyell, 

 with the assistance of MM. Nyst and Bosquet, gave a list of 47 

 species of fossil shells which presented this difficulty — that whereas 

 the Faluns of Touraine do not contain a single form belonging to 

 the Nummulitic formations, even those of its latest stage, but have 

 a marine fauna, which so far as accurate identification has gone, is 

 wholly Eastern Atlantic, the reputed Bolderien Miocene fauna has 

 had assigned to it a mixed assemblage of North- Sea Crag shells, 

 (recent species), and those of the Belgian equivalents of our Barton 

 beds. It was this consideration probably which caused M. d'Orbigny 

 to refer it to his " Sous-etage Tongrien"t; indeed, it is evident 

 that it was the Bolderberg list which produced this double error. 



We collected a considerable number of the fossils of this locality. 

 They occurred, as stated by Sir Charles Lyell, in the pebble-beds 

 and associated sands, they are for the most part broken and worn, 

 and " resemble shells thrown on a sea-beach" {u. s. p. 296). The 

 great preponderance of single valves and of fragments of Pectunculus 

 glydmeris, and Crag forms of Pecten, Venus, (fee, gives to the assem- 

 blage the aspect of the Scaldesien fauna ; but with these are Diestien 

 forms of Lunulites, Flabellwm, and the little Oliva jiammulata, all 

 exceedingly well preserved. Even at first glance the fauna of the 

 Bolderberg sands is to a very great extent identical with that of the 

 Belgian Crag. 



Sir Charles Lyell's list, when cleared of all species respecting 

 which doubts were felt, leaves 23 forms. M. Nyst's more recent list 

 also contains 47 species, but differing from the 47 given by Sir C. 

 Lyell. Taking the first list, some of the identifications were erro- 



* Quart. Joui'n. Geol. Soc. vol. viii. p. 279. 

 t Cours Elem. de Paleont. &c. t. 11. p. 764. 



