1809.] 
Trapp, which, in the Swedish language, 
signies a ladder. In these basaltic 
masses, balls of the same matter, com- 
posed of concentric coats, are frequently 
found. 
The rag-stone has been accurately ana- 
lyzed by Dr. Withering, who found 
that one,thousand parts of it contained 
four hundred and seventy-five parts of 
siliceous earth, three hundred and twenty- 
five argillaceous earth, and two hundred 
calx of iron. But this iron seems.to me 
to be in a small degree of calcination ; 
from the dark blue colour of the stone, 
from the rusty colour it assumes on 
being exposed to a further state of cal- 
cination by air and water, and from the 
magnetic property of the mountains, 
which, as Dr. Plot observed, turned the 
needie 6° from its proper direction. 
This magnetic property has been since 
observed in several basaltic mountains, 
particularly in the Giant’s Causeway, in 
Ireland; and very remarkably in a ba- 
saltic columnar mountain, called Compass 
Hill, in the island Cunnay, one of the 
Hebrides, described by George Demp- 
ster, esq. in the Transactions of the So- 
ciety of Antiquaries in Scotland, vol. i. 
Of the Fractures and Dislocations, called 
Faults of the Coul, and accompanying 
Strata; with some Conclusions and 
Conjectures respecting the Formation 
of Coal, Lime-stone, and Basaltic- Hills. 
i have, in the beginning, represented 
the coal, and accompanying strata, as 
rising up to the lime-stone hills, and 
to. Wednesbury, and Netherton-hills, 
(which I think aré probably lime-stone 
at their foundation,) and in general, to- 
wards the extremity of the coal country, 
where they crop out to day, and are lost. 
Bat this is to be understood as a general 
consideration of the position of the coal 
and strata through the country, referable 
to many great and Jocal irregularities, 
to sudden risings and fallings of the re- 
spective strata, which are sometimes of 
a greater extent, by which the stratum 
of coal is broken, or its direction altered 
in various ways. These irregularities 
occasion much difficulty and disappoint. 
ment to the working of mines, especially 
when the fracture is considerabie, and 
the fall of coal, or the stratum, is great, 
that it cannot be worked upon the level 
of the engine-pit, and consequently the 
water cannot be dramed by the means 
prepared for it. 
The fractures, or fissures, are of va- 
rious lengths, from a few yards to one 
Minéralogy of the South-West of Staffordshire. 
AEF: 
or more. miles; and the Fall, or Trap-: 
ping Down (as itis sometimes called}, 
of thé coal and other contiguous strata, om 
one side of the fracture, below the core 
responding strata on the other side, is 
from a few inches-to sixty, eighty, or one 
hundred yards. When there is no in- 
tervening matter, between the two faces 
of the fracture, it is called a Slip, and 
these faces, which have the same corre= 
sponding obliquity of direction, show a> 
smoothness and polish which they seem 
to have acquired, by the force with which 
they have been rubbed against each 
other, ‘To these surfaces, the col- 
liers give the name of Glass Faces. 
But when the fracture and fall are cons 
siderable, there is generally an interval, 
or space between the two corresponding 
faces ; which space is filled up with soma 
argillaceous matter, or more frequently 
with roach, which is called a fazult.* 
This fault has the same oblique direc- 
tion as the faces of the fracture, and 
extends through the strata.to unkzown 
depths. The coal which has been thus 
interrupted, and which has fallen to its 
former level, generally proceeds in the 
same, or nearly the same, inclination; 
that is, it continues to rise, or dip nearly 
to the same point of the compass, as it 
did on the other side of the fault, though 
not always with the same rapiditys 
There are, however, exceptions to this 
rule. At least, there is one very re- 
markable instance of a great fault near 
Bilstone, where the inclination or dip of 
the coal is quite reversed by the fault, 
The rock which eomposes the fault. of 
this country, is white, and consists of 
argillaceous and siliceous earths; but 
in some other countries, the fissures, not 
only of coal, bat also of other strata, are 
filled up with basaltes, or whin-stone, 
and are called Whin-Dykes in the nor= 
thern parts of this island.—See a curious 
account of the Whin-dykes, which in« 
tersect the strata in some parts of Scota 
land, by Mr. Mills, Phil. Trans. 1790. 
Various opinions have been formed 
respecting the formation of coals. Sonje 
Sa a a Ra a 
* The word favit, in this sense, seems to 
be derived from faille, which has _the same 
signification in the country of Liege, whence, 
it is probable, we derived the art of working 
coal-mines, as those of Liege are the 
most ancient in Europe. Faille, evidently 
comes from faillir, to fail, because at these 
faults, the coal fails, or is interrupted. 
Hence, probably, the expression, ‘* to be at 
a fault,” when we can proceed no farthe@ 
with any kiad of work, 
consider 
