THE OLD RED SANDSTONE. 951 
The curtain again rises. A last day had at length come 
to the period of the middle formation; and in an ocean 
roughened by waves, and agitated by currents, like the ocean 
which flowed over the conglomerate base of the system, we 
find new races of existences. We may mark the clumsy 
bulk of the Holoptychius conspicuous in the group ; the shark 
family have their representatives as before ; a new variety of 
the Pterichthys spreads out its spear-like wings at every 
alarm, like its predecessors of the lower formation ; shoals of 
fish of a type more common, but still unnamed and unde- 
scribed, sport amid the eddies; and we may see attached to 
the rocks below substances of uncouth form and doubtful 
structure, with which the oryctologist has still to acquaint 
himself. The depositions of this upper ocean are of a mixed 
character: the beds are less uniform and continuous than:at a 
greater depth. In some places they consist exclusively of sand- 
stone, in others of conglomerate ; and yet the sandstone and 
conglomerate seem, from their frequent occurrence on the 
same platform, to have been formed simultaneously. The 
transporting and depositing agents must have become more 
partial in their action than during the earlier period. ‘They 
had their foci of strength and their circumferences of com- 
parative weakness; and while the heavier pebbles which 
composed the conglomerate were in the course of being de- 
posited in the foci, the lighter sand which composes the sand- 
stone was settling in those outer skirts by which the foci were 
surrounded. At this stage, too, there are unequivocal marks, 
in the northern localities, of extensive denudation. The older 
strata are cut away in some places to a considerable depth, 
and newer strata of the same formation deposited unconforma- 
bly over them. There must have been partial upheavings 
and depressions, corresponding with the partial character of 
