SILURIAN PERIOD 
And many a throne, in many a sea and clime, 
Has she set up, and levelled in her time. 50 
Within our range as yet the waters through, 
Invertebrates alone have come in view : 
Holding the scene through deep and shallow seas, 
In classes, orders, genera, species. 
But now backboneless life has ceased to be, 5 c 
Wide though its ranks, sole tenant of the sea. 
Creatures of sterner build are now abroad, 
Whose bodies, furnished with a notochord, 
Or with developed column vertebrate, 
Proclaim Life risen to a higher state. 60 
Whence came these fish-like creatures, who can say ? 
Doubtless in forms of lower life there lay 
The power to rise to this. Sea-squirts and worms 
Perchance were first in front, or some such forms. 
Still be what may their doubtful pedigree, 65 
Creatures of fish-like build now swim the sea. 
Small Ganoid forms, in bony armature, 
(Allied, perchance, to Lampreys), wander here. 
Furnished they are with plate-like looking scales, 
Small single fins, and back-bone stiffened tails. 70 
And some of higher form are in the tide, 
Seeming to Birchir fishes close allied. 
And creatures larger framed, with prickly skin, 
Dog-fish and Shark like also haunt the scene. 
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