128 
Some of the beds of rock are coarse grained, while others 
are of a finer texture, and in the upper part of the series thin 
beds of conglomerate exist similar in nature to those found in 
the Old Red Sandstone, from the debris of which, doubtless, it 
was formed. The rounded pebbles of Quartz and Felspar con- 
tained in them are cemented together with fine particles of silici- 
ous, argillaceous, and ferruginous elements of a very tenaceous 
character. The shale, clay, and marle beds of this series pre- 
dominate to a greater extent in some parts than in others. 
The thickness is also variable as we proceed in depth, for we 
find that some of these beds are in a more compact and rocky 
condition at deeper levels. The prevailing colours of the shale 
and marle beds are reddish, brown, dark purple, dingy yellow, 
chocolate, and claret. The distribution of a very large quantity 
of peroxyde of iron, held in solution during the period of the 
formation of these rocks, imparted the colours we now observe 
in them. This is beyond doubt, for we find deposited Hematite 
iron-ore of an excellent quality in this series and at some places 
such as at Saint Annals Iron Mine, China-Blind Meend, and to 
the Southern extremity of the Lower Oakwood Iron Mine 
level. In former years, ore of a poorer quality was also worked 
at the Southern extremity of Ruspidge Meend, near to Shake- 
mantle. It has not, however, been worked in a general 
manner, or even searched for, a circumstance which has arisen 
chiefly because immense deposits of Hematite iron-ore have been 
found, and worked all round the Forest in the Carboniferous 
Limestone, situate at the base of the Millstone Grit. 
Comparatively little water finds its way into the Mill- 
stone Grit series, because the beds of clay and shale act as a 
dam, throwing off the greater portion of the water periodically 
due to rainfall. The thickness of the Sandstone or Millstone 
Grit series varies in different parts of the Forest, and it has 
been stated to be from 273 to 455 feet. 
At the Parkhill Colliery adit the thickness of the Millstone 
Grit, measured from the Lower Trenchard coal to the upper 
side of the Carboniferous Limestone, is 612 feet. 
