DEPOSITS OF THE LEEN VALLEY 
77 
gets thicker as we follow it clown into the narrow strip of flat meadow 
ground through which the Leen now meanders. This fact itself 
would suggest that the bottom of the valley probably contains a good 
thickness of gravel along with sand and silt brought down by the river. 
It must not be inferred, however, that the gravel that covers the sides 
of the valley is exactly the same in character or was formed at the 
same time and by precisely the same agency as the gravel in the 
bottom of the valley. Even the gravel and sand that is spread along 
the valley slopes is probably not all of the same age. Excavations 
made in the meadow ground that immediately borders the river show 
that our supposition as to the thickening of the gravel as we approach 
the river is quite true, and that in fact the meadow itself owes its 
flatness to the layers of sandy, gravelly, and clayey materials of which 
it is composed. But where did all the gravel come from; and how did it 
get spread along the sides of the valley high above the level of the river 
as we now find it ? 
The pebbles most abundant in these gravels of the Leen Valley are 
quartzites of all sizes, many of them split, perhaps by intense frost, 
some perhaps by the pressure of glacier ice ; but there are besides 
quartz, coal measure sandstone, millstone grit, chert, flints, and more 
rarely pebbles co'mposed of the harder rocks of the neighbourhood. An 
examination of the rocks out of which the Leen Valley has been 
scooped shows that the pebbles in the valley gravels could not all have 
been derived from the rocks that bound the valley. The valley of the 
Leen has been worn for the most part out of the Lower Mottled Sand¬ 
stone of the Trias, as may easily be seen by the little low cliffs of 
bright crimson sandstone which have been formed by th^dver here 
and there along its east bank. Now, the Lower Mottled Sandstone 
contains only a few small pebbles, so that they could hardly have been 
derived from the wearing away of this rock. In some parts of its 
course, indeed, the Leen has entirely swept away the thick mass of 
this Lower Mottled Sandstone that once stretched across its bed and 
far away over the ground beyond, and has even eaten its way down 
into the Middle Marl of the Permian, and through that again into the 
underlying Permian Magnesian Limestone, which, along with a small 
strip of Coal Measures, form its western slopes. But there are very 
few pebbles to be found that have been derived from these rocks. The 
majority of the pebbles were no doubt derived from the wearing away 
of the Bunter Sandstone, which forms so much of the country to the 
north-east. But most of the others were in all likelihood brought 
from North Derbyshire, while the flints must of course have come out 
of the Chalk. Many of the pebbles now found in the gravel of the 
Leen Valley, then, must have come a very long way. One of the 
questions we shall have to try to solve is, when and by what means 
these pebbles were brought. 
Until lately, our knowledge of the gravelly deposits that line 
the Leen Valley was confined to what we could make out from 
examining the gravel that mantles the valley slopes. Although 
