98 THE ASTEROLEPIS, 



dissimilarity in even the most perishable parts of the most 

 ancient of the ganoids 1 



I must advert, in passing, to a peculianty exemplified in 

 the state of keeping of the bones of this ancient ganoid, in 

 at least the deposits of Orkney and Caithness. The original 

 animal matter has been converted into a dark-coloured bitu- 

 men, which in some places, where the remains lie thick, per- 

 vades the crevices of the rocks, and has not unfrequently been 

 mistaken for coal. In its more solid state it can hardly be 

 distinguished, when used in sealing a letter, — a purpose which 

 it serves indifferently well, — from black wax of the ordinary 

 quality ; when more fluid, it adheres scarce less strongly to 

 the hands than the coal-tar of our gas-works and dockyards. 

 Underneath a specimen of Asterolepis first pointed out to me 

 in its bed among the Thurso rocks by Mr Dick, and which, 

 at my request, he afterwards raised and sent me to Edinburgh, 

 packed up in a box, there lay a quantity of thick tar, which 

 stuck as fast to my fingers, on lifting out the pieces of rock, 

 as if I had laid hold of the planking of a newly tarred yawl. 

 What had been once the nerves, muscles, and blood of this 

 ancient ganoid still lay under its bones, and reminded me of 

 the appearance presented by the remains of a poor suicide, 

 whose solitary grave, dug in a sandy bank in the north of 

 Scotland, had been laid open by the encroachments of a river. 

 The skeleton, with pieces of the dress still wrapped round it, 

 lay at length along the section ; and, for a full yard beneath, 

 the white dry sand was consolidated into a dark-coloured 

 pitchy moss, by the altered animal matter which had escaped 

 from it percolating downwards, in the process of decay. 



In consequence of the curious chemical change which has 

 thus taken place in the animal juices of the Asterolepis, its 

 remains often occur in a state of beautiful preservation : the 

 pervading bitumen, greatly more conservative in its effects 

 than the oils and gums of an old Egyptian undertaker, has 



