244 THE OLD RED SANDSTONE. 
Let us attempt bringing our knowledge of the present to 
bear upon the past. The larger crustacea of the British seas 
abound most on iron-bound coasts, where they find sheltering 
places in the deeper fisures of sea-cliffs covered up by kelp 
and tangle, or under the lower edges of detached boulders, 
that rest unequally on uneven platforms of rock, amid for- 
ests of the rough-stemmed cuvy. We may traverse sandy 
or muddy shores for miles together, without finding a single 
crab, unless a belt of pebbles lines the upper zone of beach, 
where the forked and serrated fuci first appear, or a few 
weed-covered fragments of rock here and there occur in 
groups on the lower zones. In this formation, however, the 
bottom must have been formed of mingled sand and mud, 
and yet the crustacea were abundant. How account for the 
fact? There is, in most instances, an interesting conformity 
between the character of the ancient rocks, in which we find 
groups of peculiar fossils,and the habitats of these existences 
of the present creation which these fossils most resemble. 
The fisherman casts his nets in a central hollow of the Moray 
Frith, about thirty fathoms in depth, and draws them up feul 
with masses of a fetid mud, charged with multitudes of that 
curious purple-colored zodphyte the sea-pen, invariably an 
inhabitant of such recesses. The graptolite of the most 
ancient fossiliferous rocks, an existence of unequivocally the 
same type, occurs in greatest abundance in a finely-levigated 
mudstone, for it, too, wasa dweller in the mud. In like man- 
ner, we may find the ancient Modiola of the Lias in habitats 
analogous to those of its modern representative the muscle, 
and the encrinite of the Mountain Limestone fast rooted to 
its rocky platform, just as we may see the Helianthoida and 
Ascidicida of our seas fixed to their boulders and rocky 
skerries. But is not analogy at fault in the present instance ? 
