214 Dr Hrssert on the Limestone of Burdiehouse, 
the neighbourhood of Glasgow, and im the districts of Cupar, 
Errol in Perthshire, East Calder, and Musselburgh ; also in the 
coal-fields of Northumberland, of Yorkshire, and of North Wales. 
It amounts only to a probability, that remains of the Megalich- 
thys have been found in certain limestones of Ashford, in Derby- 
shire, and of Northumberland. The details of these discoveries 
are given in the note appended to this section. 
M. Acassiz has stated his opinion, that there exists in Scot- 
land another species of Megalichthys, of which some relics were 
placed in his hands by Mr Rostson, who had procured them 
from Greenside near Glasgow. He conceives that the animal to 
which they may be referred, is to be distinguished from that of 
Burdiehouse by the form of the teeth, which is more compressed 
and very sharp at the edges. He proposes to call it the Mrca- 
LICHTHYS FALCATUS. 
NOTES TO SECTION XII. 
If it be allowable to suspect that the scales of the Megalichthys have been mis- 
taken for those of saurian reptiles, as was the case in the first instance at Burdie- 
house, the evidence with regard to other localities in which the remains of the Mega- 
lichthys have been found, becomes multiplied. 
The black limestone, as it is called, of Ashford in Derbyshire, so named from 
the bituminous matter which is diffused through a great part of it, rather affords 
evidence of its having been the deposit of an estuary than of a fresh water river, 
or lake, such as the limestone of Burdiehouse is supposed to have been. This fact I 
shall endeavour to substantiate hereafter. It is sufficient at present to state, that 
the limestone of Ashford contains, along with marine shells and corallines, various 
remains of the plants common in coal-fields. 
In this limestone Mr Wuirruvrst, who wrote his well known ;Theory of the 
globe in the year 1778, found, as he stated, the impression of a crocodile. Mr 
Wuirtre Watson of Bakewell conceives that Mr Wuitenurst mistook for these re- 
mains a large orthoceratite ; but, with all due deference to my old acquaintance, I 
am inclined to doubt the legitimacy of this explanation, from having myself lately as- 
certained that remains of very large fish existed in this limestone, which, if not of the 
Megalichthys, assimilated themselves to other remains found at Burdiehouse ;—this 
being a fact which had been previously unknown. It seems then atleast a plausible 
conjecture, that some remains of a large sauroid fish might have turned up in this 
locality. 
This suspicion meets with additional support from a passage which we find in 
