30 SKETCH OF THE GEOLOGY OF DERBYSHIRE. 
mountain limestone. After the magnesian limestone was deposited, 
this sea contained nothing but sand and pebbles, or at least nothing 
that has come down to us ; great beds of sand, full of round pebbles, 
which must have been swept in by very strong currents, are the 
only things it deposited. At this period we may suppose the hills 
of Derbyshire on the one hand, and those of Leicestershire on the 
other, to have been dry land, or at least a very shallow sea, studded 
perhaps with islands, while between them ran a deeper straight, in 
which the sea deposited its sand, and afterwards the marls and gyp- 
sum. These beds, forming what we call new red sandstone, never 
reach above a certain level, but sweep round the outskirts of the 
high lands, and conceal with their horizontal strata all the hollows 
and inequalities that, but for them, might exist in the intermediate 
spaces. ‘They are never, moreover, broken by the faults and disloca- 
tions that affect the inferior beds, which shew all these breaks to have 
happened between the period of the deposition of the coal measures 
and that of the new red sandstone. As to the history of the district 
since the new red sandstone period, we are left altogether to conjec- 
ture; we only know that in other places the rest of what are called 
the secondary rocks, and all those called tertiary, have been depo- 
sited. Both of these contain several systems of rocks, each requir- 
ing periods of time for their formation proportionate to the vast 
mass of materials of which they are composed, and to the numerous 
and great changes which have taken place in organic life during 
their deposition. At a very recent period (geologically speaking) a 
deposit has taken place over part of the district, more especially the 
S. of loose and water-worn materials, the broken fragments of 
sometimes distant rocks forming what is termed the diluvium. The 
precise method, however, by which this transport took place, any 
farther than that it is undoubtedly due to strong currents of water, 
is uncertain. Ata period about the same as this we know parts at 
least of Derbyshire, in common with much of the rest of England, 
to have been the habitation of the Mammoth, the Rhinoceros, and 
numerous other animals that are now entirely extinct, or confined 
to other regions of the earth. From the close of this last period the 
history of the district becomes identified with that of the human 
race. Man comes to take possession of the lands thus wonderfully 
formed, and thus admirably adapted for his convenience. He is 
content for a time to enjoy the advantages afforded him by the 
structure of the earth and the disposition of the materials, so highly 
conducive to his comforts and enjoyment, without a thought as to 
