in the Neighbourhood of Edinburgh. 187 
which has not a little contributed to solve some important questions which the osseous 
relics of the quarry have suggested. 
While Mr Rosison was thus rendering the most valuable assistance in the com- 
mon object which we had in view, this co-operation was the means of affording me 
the more leisure to satisfy myself regarding other questions of geological interest sug- 
gested by these researches. 
SECTION VI._THE GENERA OF FOSSIL FISH DISCOVERED AT BURDIEHOUSE. 
The fish discovered at Burdiehouse will be described after 
the system of M. Acassiz, Professor of Natural History at Neu- 
chatel, whose “ Recherches sur les Poissons Fossiles,” is already 
familiar to most geologists. They will also be noticed in con- 
nection with the judgment passed upon them from personal in- 
spection by this eminent naturalist; and, in availing myself of 
the kind assistance which he has thus rendered me, I would con- 
fess to an obligation for which I am truly grateful. 
M. Acassiz’s system, as is well known to those who may have 
but glanced at his work, while it carefully includes the distinctions 
which prevail in older recognised systems, gives a characteristic 
pre-eminence to that portion of the structure of the fish, which 
with geologists ought to claim a leading consideration. The skin 
of the fish connects the animal with the medium in which he 
lives. It is the essential character of the skin to form a sort of 
external skeleton, which protects its surface. Its epidermis may 
be considered, in the most general point of view, as a membra- 
nous layer of horny substance, which covers the whole surface of 
the animal, which isolates it from the external world, which 
shelters the more delicate part of its organization, and which, as a 
bad. conductor of heat, preserves to it that degree of internal tem- 
perature which is essential to its vitality. While this covering is 
composed of a number of layers, or folia, superimposed upon and 
strongly adhering to each other, it is at the same time insensible. 
and is reproduced with ease.— Recherches sur les Poissons Fos- 
siles, tom. i. p. 26, &c. 
Aa 
