232 
THE DOVER COALFIELD. 
Oct., 1890. 
of its sides, causing a lofty escarpment, which has been since 
removed by denudation ; but such an escarpment would, it has 
been observed by M. Burat, have formed a regular mountain 
chain of at least 1,000m. in height, which we are to suppose 
to have disappeared, and its site since then to have been 
covered by cretaceous beds. M. Burat suggests a simpler 
explanation, viz., that the displacement of the axis, causing 
more recent deposits to overlap the edges of others previously 
thrown down, is sufficient to explain the arrangement of the 
coals, and he says that such a displacement has been proved 
to exist in other basins, such, e.g., as that of the Loire. 
Apart from this, the fault on which the denudation hypothesis 
rests, is not found at Mons, where the bituminous coals are 
found on the southern border of the area, as at Valenciennes. 
That part of the coal measures which lies between 
Quievrain and the Douai district forms a special basin, to which 
the name “ Bassin du Nord” is given, in which both the 
sequence and character of the coal seams are pretty regular. 
Along the northern boundary we find unproductive grits and 
sandstones, followed by anthracites, having a dip of about 30° 
to south, and the beds succeed each other as they crop out in 
passing from the north limit towards the axis of the basin. 
These coals follow the edge of the basin, and can be traced 
from France into Belgium, where they are worked at Beau- 
dour, Sirault, and Bernissart, and also at Fresnes and Vieux 
Conde. More to the west, they are found at Hasson and 
Marcliiennes, and probably extend into the northern part of 
the Aniclie area. At Vicoigne as many as fifteen principal 
seams are present over an area of 1,300m., and the united 
thicknesses of which are 9'75m. 
Along the central axis of this northern basin are found the 
series of coals called by the French geologist “ demi-grasses,” 
twenty-four distinct seams of which are worked at Thiers, 
Chauffour, S. Louis, Keussite, Casimir Perrier, and Haveluy. 
Beyond Anzin and Denain these coals are got at Aniclie, and 
beyond that place at Escarpelle. From Thiers to Casimir 
Perrier, a length of 30k., this series of coal seams is cut off 
by the fault previously mentioned, and which is known as the 
“ Faille au pli,” or “ Cran de retour,” to the south of which, 
as we have seen, the coals are bituminous ; this fault dividing 
the bituminous coals from the anthracites on the north of it, 
and bringing the anthracites, which lie in regular beds, against 
the bent and folded seams of the southern area. As Aniclie 
is approached this fault is lost. 
We may pass on now towards the north-west, and come 
again to the coalfield of the Pas de Calais, which forms the 
Continental extremity of the northern coal basin. 
