IRONSTONE FORMATION OF THE FOREST OF DEAN. 271 
consideration of the petrological conditions under which they are found. 
By referring back to the arrangement I have sketched at page 225, 
of the marine carboniferous series (limestone), it will be seen that 
the ironstone formation caps division No. 3, and is immediately 
overlaid by the White Head limestone. (See also the section, page 
226.) The White Head limestone is a regularly stratified rock ; the beds 
are often highly crystalline, and do not contain, as far as I am aware, 
any fossils. The limestone rocks and calcareo-argillaceous shales below 
the ironstone formation comprises the grey and red beds, which are also 
regularly stratified, but contain, as already described, a moderate quantity 
of organic remains. I draw attention to this fact of the rocks above and 
below the "Mine Measures" being regularly stratified, because in the 
whole extent of this formation, which has an average vertical thickness 
of twenty-five yards, not one single instance of lamination or " bedding" 
has been detected. The entire mass forms a single bed, so to speak, of 
cavernous limestone, the caverns being filled with the crystallized and 
powdery haematite-ores which have been described. This limestone is 
locally called "crease," and is traversed by innumerable small joints, 
which exhibit such a total want of symmetry in their arrangement as 
to render it impossible to attribute their origin to any force acting in 
any given direction. In one spot, one set of joints will run with sufficient 
regularity over a short distance to be easily mistaken for planes of 
stratification ; at another spot another set will exhibit the same appear- 
ances, but in a totally difi'erent direction ; and both, within a very 
limited area, will be gradually confused and obscured by a third set 
cutting them promiscuously. The resemblance in these joints to what 
may be observed in highly crystalline igneous rocks, such as granite, 
where they owe their existence probably to an internal shrinking in the 
consolidation of the mass, is worthy of remark. The worked-out spaces 
in the " Mine Measures " in which the ore has been removed, and the 
limestone buttresses, or " crease," alone left standing, forming natural 
pillars and arches, remind one of the crypt of & cathedral — or, as the 
caverns occupy somewhat parallel positions in the bed, a series of crynts 
piled one over the other : indeed, the rude symmetry which in many 
places is maintained in the position of the buttresses and the regularity 
of the passages, render it difficult to, at once, disarm the mind of the 
fact of the non-existence of any artificial means, beyond removing the 
ore, having been employed in producing the illusion. Connected 
