80 THE OLD RED SANDSTONE. 
process seemed almost mechanical, so little did it employ the 
attention, and so invariable were the results. The fossils of 
the surrounding bed always found their places on the huge 
stone in three groups, and at times there was yet a fourth 
group added — a group whose organisms belonged not to the 
animal, but the vegetable kingdom. What led to the arrange- 
ment, or in what did it originate? In a principle inherent in 
the human mind —that principle of classification which we 
find pervading all science — which gives to each of the many 
cells of recollection its appropriate facts — and without which 
all knowledge would exist as a disorderly and shapeless mass, 
too huge for the memory to grasp, and too heterogeneous for 
the understanding to employ. I have described but two of 
the groups, and must now say a very little about the principle 
on which, justly or otherwise, | used to separate the third, 
and on the distinctive differences which rendered the separa- 
tion so easy. 
The recent bony fishes are divided, according to the 
Cuvierian system of classification, into two great orders, the 
soft-finned and the thorny-finned order — the Malacopterygit 
and the Acanthopterygit. In the former the rays of the fins 
are thin, flexible, articulated, branched: each ray somewhat 
resembles a jointed bamboo ; with this difference, however, 
that what seems a single ray at bottom, branches out into 
three or four rays a-top. In the latter, (the thorny-finned 
order,) — especially in their anterior dorsal, and perhaps anal 
fins, — the rays are stiff continuous spikes of bone, and each 
stands detached as a spear, without joint or branch. The 
perch may be instanced as a familiar illustration of this order 
—the gold-fish of the other. Now, between the fins of two 
sets — shall I venture to say orders ? — of the ichthyolites of 
the Lower Old Red Sandstone, an equally striking difference 
