262 Dr Hiszerr on the Limestone of Burdiehouse, 
the period when the Megalichthys lived;—to movements by 
which land rose from some large lake, only to be again submerged, 
and by which alternations of submersion and emersion were often 
repeated. During such a state of our planet, lungs might have 
been given to sauroid fish, with the view of enabling them to 
support for a continuance the changes of element to which they 
were liable ;—that when they were left dry, they might be en- 
abled to maintain life until again floated,—either by rains, or by 
the renewed effect of geological agency. 
There is also another circumstance to be kept in view, name- 
ly, that as the remains of the Megalichthys are found in bitu- 
minous shale, and even in coal itself, it is evident that the animal 
must have frequented shallows, and wet marshes, among which he 
would have been liable to be left dry, and consequently to perish, 
unless for the provision of lungs. 
That fish with analogous habits exist at the present day, may 
be learned from Dr Hamiiron’s account of the scaly Cobojius of 
India, which lives among the extensive marshes of the Yasor 
district. This fish is possessed of great tenacity of life in the 
open air; he is enabled to live many days without water ; and he 
is even endowed with a considerable facility of progressive mo- 
tion on land. 
NOTES TO SECTION X. 
A speculation has been recently thrown out, which connects itself rather with 
the character of the watery fluid, than of the atmosphere in which these sauroid fish 
lived. Upon this subject, M. Acasstz has remarked, that if structure be indicative 
of habit, this sauroid tendency of the fish of the limestone of Burdiehouse will lead 
to further discoveries of the aqueous fluids of the globe, which were neither salt nor 
fresh; as, by the character of the vegetation of remote periods, naturalists have 
been led to deduce a difference in the gaseous constitution of the atmosphere.— 
(Report of the Edinburgh Meeting of the British Association of Science. ) 
With regard to this observation I would suggest, that the argument regarding 
a half-saline state of waters, considered as prevailing over the whole ancient surface 
of the globe, is unsatisfactory, so long as it can be shewn that two distinct species of 
deposits, one apparently fitted for marine, and the other for fresh-water life, have 
existed. Proofs of this coexistence form the leading object of investigation in the 
present memoir. 
5 
