242 SILUEIA. [Chap. X. 
sparingly. We may therefore fairly regard the Silurian system, on the j 
whole, and certainly all the Lower Silurian, as representing a long and 
early period in which no bony vertebrated animals had been called into 
existence. 
But here we must recollect that, when first created, the Onchus of the 
uppermost Silurian rock was a marine Pish of high and composite 
order, and that it exhibits no symptom whatever of transition from a 
lower to a higher grade of the family, any more than the Crustaceans or the 
Cephalopods and other Shells of the lowest fossiliferous rocks, all of which 1 
offer the same proofs of elaborate organization. Nor does the structure of 
Pteraspis, which must now be regarded as the earliest known British genus, 
since it occurs in the Lower Ludlow rock, offer, in Professor Huxley's 
opinion, any evidence of having occupied a lower position in the scale 
than existing Ganoid or possibly Siluroid Pishes. In short, the first 
created Fish, like the first forms of those other orders, was just as mar- 
vellously constructed as the last which made its appearance, or is now 
living in our seas. 
In a word, the geologist who stands on the summit of the Silurian rocks 
of Shropshire and Herefordshire, where they graduate imperceptibly into 
the Old Red Sandstone, and casts his eye westward over the mountains of 
Wales, sees before him ancient masses in which, though replete with 
copious animal remains (the tenants of preexisting shores and deep sea- 
bottoms), no traces of Yertebrata have ever been detected. Looking 
eastward, on the contrary, hills of red sandstone appear, the lower strata 
of which immediately succeed to the fish-beds of the Ludlow rocks ; and in 
those he finds that Pishes are the characteristic fossils. 
Examining upwards from that first great piscina of by-gone days, the 
Old Eed Sandstone or Devonian, which will be considered in the next 
Chapter, he ascertains that the superjacent and younger strata, whether 
Primary, Secondary, or Tertiary, are all characterized by containing 
Ichthyolites. In other words, the three or four peculiar Pishes just 
enumerated may be viewed as the heralds which announced the close of ' 
the Silurian era in Britain, and the advent of the numerous other families 
of this class, which thenceforward are found in all the younger sediments. 
The name ' Silurian ' marks, therefore, a vast series of fossiliferous de- 
posits, throughout the great mass of which no remains of vertebrated 
bony animals have been discovered. 
