154 



arranged iu plates, bars, aud scales, and sometimes all conjoined : this 

 extraordinary outward protection has given rise to curious speculations. 

 Fish, it is said, of all known existing creatures, are best enabled to 

 endure high temperature. Dr. Buckland suggests that the seas of the 

 period of their existence were of a high temperature, and consequently 

 this armour became necessary for their existence. This hypothesis 

 obtains support from another striking characteristic of the fish of this 

 type, viz. the heterocercal or unequally lobed tail, which is invariably 

 found united to the strong cuirass. It has also been remarked that, 

 with the general disappearance of this singular structure, we find, in 

 the lignites of the lias of Cromarty, unmistakable evidence of change 

 of seasons, and alternations of heat and cold. 



These lignites shew distinctly marked annual rings, as in the trees 

 of present growth ; but in the lignites, contemporary with the iclithyolites 

 of this ancient type, annual rings are cither absent, or faint and unfre- 

 quent ; and here, says Hugh Miller, "just ere winter began to take its 

 place amongst the seasons, the fish fitted for living in a highly heated 

 medium disappeared ; they were created to inhabit a thermal ocean, 

 and died away as it cooled down." 



I perhaps may be permitted to speculate on the causes and intents 

 of this sin^^ular arrangement, although I do so with deference and 

 doubt. In my observations I shall adopt what appears to me a sound 

 mode of reasoning — analogy. It may appear that the peculiar causes or 

 circumstances under wliich these fish existed in the old red are widely 

 different from any that at present present themselves ; but on considera- 

 tion it must be admitted that the variation is not much, if any, wider than 

 the flora of the coal and its present type. Now, assuming it to be true 

 that the seas of the old red period were, at certain times, of great 

 depth, at others shallow (during both of which this singular type 

 existed), strewn with the enormous sharp and angular fragments of the 

 older rocks, with the bottoms broken up and fractured by the great 

 convulsion that closed the silurian period, would not fish frequenting 

 such seas require an amount of protection in following their prey, 

 difterent from those which frequented, or were known to exist in, some 

 of the lake like seas of later periods, and where the sediment was either 

 calcareous or of an equally fine texture? Does it not strike the 

 observer, that the head of an animal frequenting such seas, to protect 

 it from injury, should be bony and buckler formed? The long tail in 

 some, and the heteroccercal tail in others, are evidently formed to 

 enable the fish to strike rapidly down iu deep water, and to rise with 

 equal rapidity ; and are not the heads so formed to protect them in 

 such descent and ascent, and to enable them to I'ootlike the dog-shark 



