50 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. 



one part the coast-line must have been much nearer than at the other, 

 and that, if we take the distance from Boulogne to Hirson at 300 

 miles, the middle portion of it is that which answers to such a 

 position. 



There are other considerations, should the foregoing not be deemed 

 altogether sufficient, which bear out the inference that the coast-line 

 to which these shingle-beds were subordinate lay to the north. 



The only test as to whether any zone of an old sea-bed is complete, 

 is the form of section it gives when measured at right angles to its 

 greatest direction, such direction being always in certain parallelism 

 with the coast-line. The littoral zone, commencing with the highest 

 marginal beds, parts gradually with its well-known characteristics, 

 and passes into the next lower zone of sands : in like manner the fine 

 earthy sediment forming clays and shales is succeeded by that of 

 lighter calcareous matter, and which from its specific gravity is 

 capable of thickening out over wide areas, so that all geological 

 groups, with a like mineral composition, when so measured, are 

 found to be great lenticular masses : and such is the form of the 

 Belgian subordinate bands. 



It has been shown that the broad range of the Ardennes acquired 

 an amount of relative elevation at some time after the completion of 

 the series above the Eifel limestone : it could not therefore have been 

 in a position to have furnished any of the materials towards the under- 

 lying conglomerate or shingle group ; and, as this zone is a perfect one, 

 the source of its materials must necessarily have been on the north, — 

 a view which is further confirmed by the character of the materials 

 which form the shingles and which enter into the composition of the 

 middle and upper palaeozoic sandstone groups. 



So much of the palseozoic series as is to be seen north of the 

 Belgian coal-field is nowhere of greater age than the middle Rhine 

 beds ; the sandstones which are subordinate to the Eifel (Givet) lime- 

 stone, those of the next higher group with Cucullcea Hardingii and 

 C trapezium, those associated with the Boulonnais coal, and with our 

 dark millstone grit series, all imply the synchronous existence of wide 

 subaerial areas composed of crystalline micaceous rocks, as well as 

 hardened and mineralized sedimentary ones. No such mineral masses 

 occur along the axis of the Ardennes or Hundsriick ranges ; and it is 

 only on the north, therefore, that they could have found a place, 

 where they may reasonably be supposed to have risen from beneath 

 the old rocks of Hal and Jodoigne. 



This old terrestrial area was a southern extension of the Scandi- 

 navian range : portions of it became depressed or broken down at 

 definite geological periods ; but subsequently to early palaeozoic times 

 it exhibited a salient mass, on either side of which the middle groups 

 had their limits (Upper Silurian and Devonian), and the existence of 

 which in parts can be traced upwards far into the tertiary period. 

 The area over which the erratics of Western Europe (Germanic area) 

 are distributed conforms to this extension of the Scandinavian range. 



Along the Ruhr the true coal-measures have a visible breadth of 

 at least sixteen miles ; they have, however, a much greater real one 



