726 REPORT—1863. 
On the Magnesian Limestone of Durham. 
By Joun Dacuisu, F.G.S., and G. B. Forster, M.A. 
CovreRinG as it does so considerable a portion of the Northern Coal-field, the 
Magnesian Limestone must always afford a most interesting study to those 
engaged in the mining operations of this district. This arises from its im- 
portant bearing not only on geological, but also on physical conditions; the 
former have long been a subject of general interest, and as regards the latter, 
one of the most marked features is the large quantity of water met with in 
the shafts which have been sunk through it for the purpose of winning the 
coal below. It was more especially to this feature that this paper was, in 
the first instance, proposed to be directed; but-in the preparation of the 
required maps and sections, it was found that allusion to other debateable 
ground could not be avoided. 
This deposit has, at various times, occupied the attention of some of our 
ablest geologists, and has been carefully investigated by them, so far as it 
can be seen in its sections open to the day; but the writers, in the pursuit 
of their professional duties, having had frequently brought before them sec- 
tions of the entire deposit in the numerous coal-shafts which have passed 
through it, and having obtained the true inclination of the Coal-measures 
underlying a large tract of the Limestone in the workings of the various coal- 
mines, have had suggested to them conclusions somewhat at variance with 
the opinions expressed by recent writers, and which they deem of sufficient 
interest to bring before this Association. 
In all the sinkings through the Magnesian limestone, feeders of water, 
more or less considerable, are met with at a certain distance from the surface, 
derived not so much by percolation through the mass of the rock—for this 
can obtain to a small extent only—but collected in and coming off the nume- 
rous gullets and fissures which everywhere intersect and divide the mass of 
strata. If the shaft be not drained by pumping, or otherwise, the water 
from these feeders rises to a point which remains, save in exceptional cases, 
constant. A line drawn between these various ascertained points gives the 
line of saturation, indicated by dotted lines, on the sections exhibited ; 
and it will be observed that, although this line commences at the sea-level, 
it neither continues on this plane nor follows the line of stratification, nor 
yet all the undulations of the surface, but rises for the most part uniformly 
with it as it passes inland. At Seaton Pit, near Seaham, it is 226 feet from the 
surface, and at Eppleton, three miles directly west of Seaton, it is the same ; 
and as the surface-level of the latter is 180 feet above that of the former, it 
follows that the line of saturation rises in this direction at the rate of 60 
feet per mile. 
It was mentioned previously that under certain circumstances there is a 
slight variation in the level of the line of saturation; this occurs sometimes 
near the outcrop of the Limestone, when after a long succession of wet weather 
the level is raised a few feet ; and, again, in some cases where gullets are ex- 
posed on the surface, down which large quantities of water from flooded 
brooks, &c., find their way, and hence in any shaft communicating with 
these gullets the water rises rapidly and considerably. 
Immediately underlying the Limestone is a bed of sandstone of very variable 
thickness, which when exposed to the action of the atmosphere disintegrates 
rapidly, and has hence acquired its local name of “ friable Yellow sandstone.” 
It is in sinking through this bed of rapidly decomposing sandstone that such 
great engineering difficulties have been encountered, owing to the enormous 
