Igneous Rocks of South Staffordshire. 525 
that in the same district the faults were not all produced at one 
period. 
Near Wolverhampton, the underground trap, which is spread over 
an area of five miles by two, is to a great extent perfectly conform- 
able to the coal-measures above and below it; but when traced for 
upwards of three miles, its nonconformity to the coal-beds becomes 
apparent, and this is further confirmed by the giving off of white 
vertical felspathie dykes, similar to those before alluded to. It is, 
however, worthy of record, that no centre of eruption has yet been 
discovered in this part of the district whence the flow of’ basaltic 
matter could have been derived, though it is believed that it may 
have proceeded from the distant Rowley Hills. 
After minutely elucidating the distinctions and the variations of 
structure and form in the various trappean rocks of this district, the 
report proceeds to point out the changes which have been produced 
in the coal-measures by their intrusion. The same beds of coal, which 
in parts of the field exempt from basalt are highly bituminous, are, 
when in contact or in the vicinity of that rock, either converted into 
anthracite or charred into cinders. In the Wolverhampton tract the 
upper portion of the coal beneath the greenstone is entirely cut out, 
whilst the lower part is converted into anthracite, and often fissured 
by vertical joints, accompanied by veins of calcareous spar; as if, 
in driving off the bituminous matter of the coal, the extreme heat 
had also occasioned a contraction of the carbonaceous mass. Be- 
sides these alterations of the coal, the beds of ironstone are equally 
affected, the clay being rendered porcellaneous, and the sandstones, 
usually much hardened, are in some cases even vitrified. 
In addition to these changes, which are analogous to effects ob- 
served in other countries, and are such asa high degree of tempera- 
ture will readily explain, other alterations are cited, with some of 
which, indeed, Mr. W. Matthews acquainted me when I examined the 
tract, and the solution of which is not so easy ; viz. that beds slightly 
impregnated with iron at a distance from them, become gradually 
more charged with it as they approach the igneous rocks, and are 
of very superior quality in their immediate vicinity. This fact, in- 
deed, is perfectly in accordance with what I have lately observed in 
the Ural Mountains, where masses of iron ore are crystalline and 
even highly magnetic when in contact with eruptive rocks. 
Another point dwelt upon, perhaps still more curious, and which 
also requires the consideration of the chemist, is, that wherever 
igneous rock is present in the neighbourhood of beds of coal, and 
yet separated from them by an intervening substance, which has 
prevented their being injured by intensity of heat, the coal is fre- 
quently what is called “brighter and more bituminous !” 
With such facts before them, the authors of this report are aware, 
that other agencies than those of mere heat, are required to account 
for the production of iron concretions and the crystalline strue- 
ture of coal; but whilst they think that electric and magnetic cur- 
rents must also have operated in bringing about some of the results, 
they are convinced that the presence of igneous matter, often ex- 
