295 
more frequently, and are generally thicker and of greater 
value than those of the Millstone Grits, As the higher 
members of the Coal Series are reached, the sandstones 
become less and less persistent, and exist only in areas of 
small extent, thinning out and giving place to shales, or 
splitting and dovetailing with strata of shale until, the latter 
gaining preponderance, the Sandstone finally disappears. 
The coals occur with greater frequency, and are thicker and 
more valuable than those of the Lower Coal-measures. The 
Upper Measures of the Yorkshire Coal Field are more broken 
by faults than those lower in the series, and as a natural 
consequence the seams of coal are correlated with much 
greater difficulty. 
The Lower Coal Measures rest on the Rough Rock con- 
formably ; and on the western side, after forming bold 
escarpments of the Elland Flag Rock, they dip gently with 
the inclination of Grits to the eastwards. From Den- 
holme, to the junction with the Permian Limestone, the 
rocks dip to the south, wdiilst in the extreme southern part, 
below Sheffield, the dip is northwards. It is thus evident 
that they form a trough or basin, with a framework of Mill- 
stone Grit Rocks. The higher beds of the Coal Formation 
form concentric circles, one within the other, whose radii 
are ever becoming smaller the nearer the top the series is 
approached. The eastern part of tbe trough is lost beneath 
the escarpment of the Permian Limestone, which bisects it in 
a north and south direction. It is, however, known to 
exist, the Limestone having been pierced in numerous 
instances to obtain the coal from the seams below. 
Some of the sandstones of the Upper Coal Measures, 
where they are in apposition to the Permian Limestone, are 
coloured red or purple, whilst in other instances they remain 
unaltered, and exhibit the ordinary colour of the rock, as 
seen further to the westwards. On Brierlcy Common, and 
