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TOPULAR SCIENCE REVIEW. 
line of strike. The Belgian coal-field is but one of a deep, long 
and narrow series, ranging from Westphalia to the north of 
France. The most easterly is that of the Ruhr, the second Ai^- 
la-Chapelle, the third Liege, and the fourth Hainault and Valen- 
ciennes ; it is then probably hidden on its north-westerly strike 
from Therouanne by the newer rocks, and its extension is proved 
by boring at Calais ; the main axis (that of Ardennes) crossing 
the Straits of Dover, passing, as before stated, south of London 
through Berks, Wilts, and into Somersetshire, there to join the 
Mendip disturbances, and on to the southern edge of the great 
and exposed Welsh coalfield, by Worm’s Head, Tenby, and St. 
David’s, determining and probably defining the boundary between 
the Marine Devonians on the south of the Mendip and Ardennes 
axis, from that of the Old Red Sandstone north of it, and the 
great Hereford and Brecknock Old Red north-west of the Severn.* 
In 1872 Professor Prestwich wrote his most able paper in the 
“ Popular Science Review ” (loc. cit .), stating therein (p. 235) that 
“ between Clan Down, near Bath, and the Well, at Kentish Town, 
no trial for coal or water had been carried to the base of the 
secondary rocks or had reached more than about 600 feet 
beneath the sea level.” Since then, not many miles north of the 
latitude of Bath, the boring at Burford, in Oxfordshire, has 
passed through the lower secondary rocks and into the Coal- 
measures, touching them beneath the New Red Sandstone at 
1,184 feet. “There can, however,” says the learned author, 
“ be little doubt of the continuity of the range of the Palaeozoic 
rocks under these newer formations from Belgium to Somerset ; 
but whether or not the coal measures were ever continuous 
between the two districts, and whether, if they were, they have 
been removed by denudation, leaving only the Lower Palceozoic 
rocks , requires further discussion.” 
Again, Mr. Prestwich, with far-seeing induction (as subsequent 
investigation has proved in Oxfordshire), discusses the question 
of the extension of the Bristol coalfield eastwards. This inde- 
pendent basin is cut off both on the east and on the west by 
ridges of Millstone Grit and Mountain Limestone — the general 
belief being that the eastern boundary limits the extension ; or 
that eastward of the north and south strike of the edge of the 
basin there are no more Coal-measures. This eastern edge is 
covered by the secondary rocks (Trias, Lias, and Oolite), thus 
causing much uncertainty as to the disposition (or arrangement) 
of Palaeozoic rocks under or east of them. 
“ Admitting,” says Mr. Prestwich, “ the basin to be complete 
and isolated, that is no proof that the older Palaeozoic rocks 
prevail exclusively or come to an end on the east side, for the 
Vide sketch-map No. 8, plate VII. 
