austen extension of the coal-measures. 47 



Belgian Area. 



The lower tertiary strata of Belgium (Nummulitic formation), 

 between Bruxelles and the great coal band, overlie a surface of palaeo- 

 zoic rocks, without the intervention of any member of the secondary 

 formations. At Tournay these tertiary strata pass over the edges 

 of the cretaceous rocks, and both are wholly unconformable with 

 the carboniferous limestone there. From Tournay by Ath as far 

 north as Hall, Wavre, and Jodoigne, there is a regular descending 

 series of palaeozoic groups, presenting a like series of undulations 

 with those to be observed on the south side of the coal-band, as from 

 Bellignies eastward, and which on that side rise into the ridges of 

 the Condros and the Ardennes. The breadth for which this con- 

 dition of surface, next beneath the Nummulitic series, can be traced 

 north of the coal-measures is about thirty miles. In an east and 

 west direction a like relation is known to exist from the meridian of 

 Namur to that of Lille, or from eighty to ninety miles, whilst the 

 trough-shaped arrangement of the coal-strata, in both directions as 

 towards Liege and Lillers, leaves no doubt whatever that this rise of 

 the older groups in the north has a much greater extension than 

 what is here assigned to it. 



A restoration of this palaeozoic surface is given in the accompany- 

 ing map (PI. I.). If, in conjunction with this representation, a line of 

 section should be drawn from the summit of the Ardennes across the 

 whole series, it would present a plane surface, with a uniform slope 

 northwards descending from an elevation of 2000 feet to somewhat 

 below the sea-level. Of this surface every part stood in a like rela- 

 tion to the secondary formations ; or, in other words, at their periods 

 the palaeozoic group north of the coal-band must have had an eleva- 

 tion equal or nearly so to that on the south, — it must have been part 

 of the same raised area, — and it must have received its relative depres- 

 sion subsequently to the secondary period and synchronously with 

 the overspread of the nummulitic group. 



By means of the well-defined boundary-line of the oolitic forma- 

 tions of the Germanic area, we can extend this old palaeozoic surface 

 further north ; and, guided by the lines of the coarse infra-liassic 

 conglomerates of Malmedy and Stavelot, we may infer that at this 

 early period the northern mass then had, relatively with the Ardennes 

 range, a somewhat higher level : the island of HeHgoland, distant 

 about 300 miles north of the locahties here in question, being the 

 nearest spot at which we are certified of the existence of any infra- 

 liassic strata* ; and where the lower beds, consisting of sands, indi- 

 cate shallow-water conditions at that time. 



The Boulonnais. 



I have elsewhere shown f that the middle and upper palaeozoic 



* Beitrage zur geofrnostischen Kenntniss des Norddeutschen Tiefland, von 

 Otto Volger. 



t Quart, Joum. Geol. See. vol. ix. p. 244. 



