IHE OLD RED SANDSTONE. 117 
suggestion which has emanated from one of the first of living 
geologists? Fish, of all existing creatures, seem the most 
capable of sustaining high degrees of heat, and are to be 
found in some of the hot springs of Continental Europe, 
where it is supposed scarce any other animal could live. 
Now, all the fish of the ancient type are thickly covered by 
a defensive armor of bone, arranged in plates, bars, or scales, 
or all the three modes together, as in the Osteolepis and one 
half its contemporaries. The one-sided tail is united invari- 
ably to a strong cuirass. And it has been suggested by Dr. 
Buckland, that this strong cuirass may have formed a sort of 
defence against the injurious effects of a highly heated sur- 
rounding medium. The suggestion is, of course, based 
purely on hypothesis. It may be stated, in direct connection 
with it, however, that in the Lias—the first richly fossilifer- 
ous formation overlying that in which the change occurred — 
we find, for the first time in the geological system, decided 
indications of a change of seasons. The foot-prints of winter 
are left impressed amid the lignites of the Cromarty Lias. 
In a specimen now before me, the alternations of summer 
heat and winter cold are as distinctly marked in the annual 
rings as in the pines or larches of our present forests; where- 
as in the earlier lignites, contemporary with ichthyolites of 
the ancient type, either no annual rings appear, or the mark- 
ings, if present, are both faint and unfrequent. Just ere 
winter began to take its place among the seasons, the fish fit- 
ted for living in a highly heated medium disappeared : they 
were created to inhabit a thermal ocean, and died away as it 
cooled down. Fish of a similar type may now inhabit the 
seas of Venus, or even of Jupiter, which, from its enormous 
bulk, though greatly more distant from the sun than our 
earth, may still powerfully retain the internal heat. 
12 
