20 SKETCH OF THE GEOLOGY OF DERBYSHIRE. 
have become more nearly exhausted. On tracing the formation into 
Nottinghamshire, it evidently becomes thinner as we proceed S. until 
about Nuthall its thickness does not exceed 30 feet; hereabouts it has 
been continually pierced, and the upper hard coal extracted from 
beneath it to a considerable extent. Between Nuthall and Bilborough, 
near a place called Chilwell Dam Farm, a small valley, through which 
a trifling brooklet runs down to the river Leen, cuts entirely through 
the magnesian limestone for 300 or 400 yards, and exposes a small 
patch of coal measures,* everywhere surrounded by magnesian lime- 
stone; and on the S. boundary of the formation, between Bilborough 
and Radford, it thins out entirely, not more than one yard of it having 
been met with in the coal pits to the S. of the road from Nottingham 
to Strelley. The extreme thinness of the magnesian limestone is, no 
doubt, partly due to denudation, some of the upper part of it having 
been washed away ; but that it never was thicker than 20 or 30 feet. 
at this end of its course, may be seen by tracing the run of the next 
superior beds, the red and white sandstone. The western boundary 
of this formation runs from about Worksop Manor, down through 
Cuckney, to the E. side of Mansfield ; thence it gradually trends to 
the W. and at Annesley it actually overlies the whole of the magne- 
sian limestone to its extreme edge, so that they both may be seen in 
one escarpment. From Aanesley it recedes again to the E. runs 
round Newstead Abbey, and thence through Paplewick, and a little 
E. of Bulwell to Bassford and Radford. From Radford its course is 
that mentioned before as the S. boundary of the coal-field. Beyond 
this, its general course, however, there are some outliers of it near the 
escarpment of the magnesian limestone. Of these, Kimberley Knole 
is one, and another may be seen in Strelley Park. Beneath these 
we may be sure we have the whole thickness of the magnesian lime- 
stone, unless (which is highly improbable) the two should be uncon- 
formable, and this thickness is certainly not more than about 80 feet. 
The entire absence, moreover, of magnesian limestone in the new red 
sandstone district to the S. renders it probable that it thinned out and 
ended originally about its present southern boundary. This being 
the case, the existence of outliers of red sandstone lying but a little 
distance above the coal measures, and within the district where coal 
* In the cutting of the new railway to Babbington Colliery the base of the 
formation is exposed, and contains some beds of a brown conglomerate, 
in which are large pebbles of mountain limestone, with crinoidal remains. 
