THE LIAS MARLSTONE OF LEICESTERSHIRE. 
63 
Marl stone as a lenticular mass of rock enclosed in the Lias 
shales. From its superior hardness, the Rock-bed has been 
able to withstand denudation to such an extent that, when 
well developed, it forms an elevated table land or terrace 
from half a mile to two miles in width, rising with a gentle 
inclination from the base of the slopes of the Upper Lias 
shales on the east, and terminating in a bold escarpment 
overlooking the Lower Lias country on the west. This escarp¬ 
ment has in many places become deeply indented by valleys, 
and carved into promontories and even outliers through the 
wearing action during the course of ages of the many streams 
that breach its face. The porosity and extensive jointing of 
the exposed Rock-bed, which rests upon comparatively imper¬ 
vious clays, render it a copious reservoir for water. Most of 
the brooks of the adjoining Lower Lias district take their 
origin in springs thrown out at its base. 
The Marlstone Rock shows great variations in mineral 
character. When quarried in an unweathered state in deep 
pits or under beds of impervious clay, it is a hard crystalline 
rock of a bluish-green tint, but where it has for a length of 
time been exposed to the disintegrating influences of the 
atmosphere it becomes, owing to chemical changes to be 
hereafter explained, of a rusty brown colour, and porous and 
friable in texture. At the surface the marlstone breaks up 
into a very characteristic deep red ferruginous soil, which 
forms an excellent corn land, and contrasts in a marked 
manner with the pasturage of the adjoining country occupied 
by the heavy clays above and below. Trees attain a large 
growth on this rock, and root-crops, as well as all the cereals, 
thrive upon it. 
In a general way the Marlstone Rock consists of two very 
distinct portions—an upper and a lower—each of which 
constitutes, roughly speaking, about half its entire thickness. 
When the rock is in an unweathered state, this distinction is 
not very obvious to the eye, though it comes out on analysis. 
In the brown or weathered condition, however, the difference 
of these two portions is readily discerned. The upper part 
then appears as a highly ferruginous laminated limestone, the 
lower as massively bedded, but softer and more or less concre¬ 
tionary sandstone. It is a noteworthy fact that only the 
upper portion of the Marlstone is sufficiently rich in iron to pay 
for working, so that even when that rock attains a thickness 
of twenty-live feet or more the ironstone beds actually worked 
will not at the outside exceed some eight or ten feet. If then 
these upper beds are absent, the Marlstone will be unproduc¬ 
tive of iron. Some beds of the Marlstone are crowded with 
