16 SKETCH OF THE GEOLOGY OF DERBYSHIRE, 
Nottinghamshire coal-field in a general sense; but were it continued 
without interruption the district would have scarcely half its present 
width, since the whole of the beds would shortly be buried beneath 
superior strata. It fortunately happens, however, that there is a con- 
siderable flexure of the beds running down the middle of the district, 
caused by a line of elevation, which runs down from a little to the E. 
of Chesterfield, by Codnor, and thence, along the valley of the Ere- 
wash, to Stapleford. Along this line the beds have been bent up, so 
as to incline from it on either hand—(see section No. 1)—forming 
what is called an anticlinal line. By the effect of this line of eleva- 
tion (which passes in the district under the name of the horseback 
fault) the beds, which had plunged to a considerable depth from their 
western boundary, are again brought up, or nearly so, to the surface, 
again to dip to the E. a little beyond; and thus a much greater quan- 
tity of coal than would otherwise be the case is kept within reach, and 
the width of the coal district greatly increased. Besides this remark- 
able dislocation, there are many other faults running across the coal- 
field. Some of these have a throw, as it is called, or produce a dis- 
placement of the beds to the amount of 270 feet, this amount gradu- 
ally diminishing, in certain directions, till the fault either disappears 
or is crossed by another. It is very remarkable, and confirmatory of 
the views before taken of the elevation of the district, that the princi- 
pal of these faults, as well as the anticlinal line mentioned above, run 
nearly N. and S. while others cross them in an E. and W. direction. 
It seems to be generally the case that, in the N. and S. faults, the 
beds on the E. side of the fault are those which are depressed, which, 
when the beds dip towards the E. has the effect of bringing the 
higher coals more to the W. or further into the field than they other- 
wise would be, which is another advantageous circumstance. Mr. 
Gratton, of Clay Cross, has published a map of considerable accuracy 
(as far as my examination has gone) of the outcrops of the five prin- 
cipal beds of coal, and several of the principal faults, but which 
requires some farther information to render it easily intelligible. 
The colours he uses represent the coals to which they are attached in 
the following section, the yellow to the E. of his map being the mag- 
nesian limestone, and a patch of green in the N.E. corner being a 
superior coal to any worked in other parts of the county. 
