UPPER A2JD LOWER. 109 



not even from the formations of the Cambrian division. " Tlie 

 Lower Silurian," says Sir Koderick Murchison, in a communi- 

 cation with which, in 1847, he honoured the writer of these 

 chapters, " is no longer to be viewed as an invertebrate pe- 

 riod ; for the Onchus (species not yet decided) has been found 

 in the Llandeilo Flags and in the Lower Silurian rocks of 

 Bala. In one respect I am gratified by the discovery ; for 

 the form is so very like that of the Onchus Murchisoni of the 

 Upper Ludlow rock, that it is clear the Silurian system is 

 one great natural-history series, as is proved, indeed, by all 

 its other organic remains." It may be mentioned further, 

 in addition to this interesting statement, that the Bala spine 

 was detected in its calcareous matrix by the geologists of the 

 Government Survey, and described to Sir Boderick as that 

 of an Onchus^ by a very competent authority in such matters, 

 — Professor Edward Forbes ; and that the annunciation of 

 the existence of spines of fishes in the Llandeilo Flags we 

 owe to one of the most cautious and practised geologists of 

 the present age, — Professor Sedgwick of Cambridge. 



So much for t\iQfact of the existence of vertebrata in the 

 Lower Silurian formations, and the argument founded on their 

 presumed absence. Let me now refer — their presence being 

 determined — to the tests of size and organization. Were these 

 Silurian fishes of a bulk so inconsiderable as in any degree 

 to sanction the belief that they had been developed shortly 

 before from microscopic points % Or were they of a struc- 

 ture so low as to render it probable that their development 

 was at the time incomplete ] Were they, in other words, 

 the embryos and foetuses of their class ] Or did they, on the 

 contrary, rank with the higher and larger fishes of the pre- 

 sent time 1 



It is of importance that not only the direct hearing^ but 

 also the actual amount, of the evidence in this case should 

 be fairly stated. So far as it extends, the testimony is clear j 



