376 
The Rev. Mr. Yates on the 
The masses, which are exposed to the weather, soon acquire exter- 
nally a yellow rusty aspect, from the combination of oxygen with 
the iron which they contain. 
The curl is here found in connexion with one stratum only. 
This is a bed of iron-stone, called the Bottom Stone of the New Mines. 
Beneath the measures, which, during a long period of time have been 
worked for coal and iron-stone in the great mining district of Staf- 
fordshire, lies a second series of strata called the New Mines , because 
they have only been worked for about sixteen years. The chief 
part of the iron-stone in this series of strata occurs in two beds of a 
few inches in thickness, which, unless so far as they are interrupted 
by faults, are supposed to extend continuously through the whole 
of this basin. The upper bed, a, (Fig. 6, Plate 38,) is called the 
top-stone, and the lower, h , the bottom-stone . They are separated 
by a bed, about two feet in thickness, of the greyish-blue slate-clay, 
which the miners call cluncb. This substance also forms beds both 
above and below the beds of iron-stone, and contains disseminated 
balls and flattened nodules of iron-stone. 
The bottom-stone is generally about four inches in thickness. 
But, at irregular intervals, it swells into great protuberances, c, c, 
which increase its thickness, in some cases, to half a yard. These 
protuberances are occupied by curl , the iron-stone remaining of the 
same thickness as in the parts where there is no curl. When the 
whole stratum has been blown up by means of gunpowder, the curl, 
as there is no natural parting, is separated from the iron-stone by 
strong blows of the hammer. The masses of curl thus attached to 
the iron-stone, and which appear to be of contemporaneous forma- 
tion, extend in very various and irregular forms through spaces 
from five yards in length to twenty yards. At the edge of the 
protuberance, the cones are small, scarce half an inch in length ; 
