60 
to a small extent^ and the ore carted down to the railway. 
The richest deposits however occur in those places where 
clay slate is overlaid with other rocks, and principally in 
the carboniferous limestone. 
In the Cleator district a narrow band of limestone, 
resting upon the clay slate, curves around the flank of 
Dent Fell, and in this narrow zone most of the iron ore 
mines of the Whitehaven district occur. The ore is found 
generally in large masses or pockets, in the body of the 
limestone, sometimes in contact with the clay slate, and at 
others filling cavities and clefts to the surface, and covered 
by alluvium. The limestone is at places overlaid by whirl- 
stone or millstone grit, and the ore occurs both above and 
below this rock. In one remarkable mine the ore fills a 
large cavity in the limestone, and is covered by whirlstone, 
which forms a perfectly even roof over a large area. Where 
the haematite occurs near the clay slate, it is generally hard 
and crystalline, and it is much softer and less siliceous 
where it appears to have been deposited in the limestone, 
or by alluvium, causing a classification in this district into 
hard and soft ores, whereas in the Furness district they are 
generally of the soft kind. 
In considering the origin of these ores, we must go back 
to the time when the limestone and associated rocks of the 
Carboniferous period had been formed at the bottom of the 
sea, and were raised therefrom by some vast force of up- 
heaval which would naturally cause great denudation and 
break up the rock into clefts and fissures. This would 
appear to have been a time of great volcanic or at any rate 
of metalliferous activity, and the two mountains of Dent 
Fell and Black Comb bear evidences of having been very 
active centres of this action, and their upheaval may very 
possibly have been connected with the eruption of the 
haematite ores. It is therefore probable that during the 
early part of the Carboniferous era, the haematite ores were 
