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great vertical range of some of the fossil species, which are found 
almost from the highest beds to the lowest of the whole series. 
Several lists of fossils are then given, in confirmation of these gene- 
ral views; and it is thence concluded, that the great sequence of 
coarse earthy schists, calcareous bands, arenaceous flagstones, psam- 
mites, &c., are the representatives of the upper Silurian system, and 
that the lowest quartzose, graywacke, flagstone, roofing-slate, &c., 
which in some places have no fossils, and in others have numerous 
repetitions of a few species of the genus Orthis, belong to the lower 
Silurian, or upper part of the Cambrian Systems. 
Part II. Older formations on the left bank of the Rhine.— The 
Hartz. Upper Franconia, &c. 
§ 1. The authors commence with a short description of the phy- 
sical region extending from the coal-field of Belgium to the south- 
eastern flank of the Ardennes, and then in like manner describe the 
country between the same coal-field and the limestone of the Eifel. 
They afterwards discuss, at some length, the methods used by Pro- 
fessor Dumont to determine the superposition of the natural groups; 
and partly from considerations derived from the symmetrical ar- 
rangement of the mineral masses, and partly from the direct evi- 
dence of sections, especially in the Hifel country, show that the 
geological sequence has been correctly determined. So far adopt- 
ing the views of Professor Dumont, the descending order in the 
provinces above-mentioned is as follows :— 
(12) Coal country.) 0/2.) a0.3 Terrain Houillier. 
(2.) Anthraxiferous country. Terrain Anthrazifera. 
(3.)' Slate country.) 42.04 Terrain Ardoisier. 
The second of these divisions is subdivided into four natural 
groups or systems, viz. Upper calcareous system; Upper quartzo- 
schistose system; Lower calcareous system; Lower quartzose-schi- 
stose system. 
The slate country is also divided into three groups,—Upper, 
Middle, and Lower. 
The order being assumed as fixed, the next question is as to the 
British equivalents of the successive divisions or subordinate sy- 
stems. 
Respecting the Belgian coal-field, there is no doubt: it is on the 
same horizon with the great coal-fields of England. Through a 
considerable part of its south-eastern boundary it is inverted, so as 
to dip under the older formations; but on a part of its northern 
boundary the older formations emerge in their regular order. 
The upper limestone of the second division is undoubted moun- 
tain limestone. The only question, then, is respecting the equiva- 
lents of the three lower divisions of the Terrain Anthraxifera, which 
are, by Professor Dumont, respectively classed with the Ludlow 
rock, Wenlock limestone, and Caradoc sandstone formations. This 
classification is not accepted by the authors, for reasons stated in 
detail. 
The upper quarézo-schistose system is separable at two parts very 
different from one another: the higher, often characterized by an 
