270 Dr Hiszerr on the Limestone of Burdiehouse 
This circumstance, also, considered as an argument, is not 
free from ambiguity. Although I conceive that, during the car- 
boniferous epoch, smaller fish dwelt more in fresh-water lakes or 
rivers, whither they were pursued by larger finny monsters, I 
should be sorry to affirm that they might not frequent estuaries, 
or arms of the sea. One genus of Palaoniscus is found in the 
limestone of Burdiehouse, and another in the later formation of the 
magnesian limestone,—which last, I presume, is of marine origin. 
5thly, Remains of fish referable to the family of the Cestra- 
ciontes (Acass.), appear both in the estuarian deposit of Ashford, 
and in the fluviatile deposit of Burdiehouse. Now, the appear- 
ance of these large finny monsters in each formation, at least 
countenances the opinion which I have advanced, that estuaries, 
as well as fresh-water lakes or rivers, were visited by them in 
quest of their prey. 
At the same time, the genera of Cestraciontes found at Ash- 
ford and at Burdiehouse, are not the same. During the spring 
of the present year, I procured large bony rays, as well as large 
palatine and maxillary teeth, from the limestone of Ashford ; but 
the bony rays widely differed from the character of such as have 
been referred to the Gyracanthus formosus of Burdiehouse. 
6thly, While the limestone of Burdiehouse encloses remains 
of the immense and scaly Megalichthys, it is only a probable con- 
jecture that similar relics might have been discovered at Ash- 
ford. (See the Notes to Section XII. of Part. I.) 
It follows from these premises, that, while a limestone which 
contains marine mollusca, &c. and, along with these remains, the 
plants common to coal-fields, together with the entomostraca of 
marshes, may be regarded as an estuarian limestone, other cir- 
cumstances, although they may point to the same conclusion, are 
either less decisive, or ambiguous. 
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