10 
from the fact, that until after the termination of the car- 
boniferous era no air-breathing vertebrated animal is known 
to have existed. For in such an atmosphere, so highly 
joaded with carbonic acid, no air-breathing vertebrated 
animal could have existed. But when this enormous 
quantity of carbonic acid had undergone fixation by 
the deposition of the mountain lime-stone rocks, and 
still further fixation, by the profuse vegetation which is 
entombed in the coal measures, the atmosphere thus purified 
may have been reduced to its present condition — to such a 
condition as to be compatible with the existence of animals 
which breathe air. Into this state the atmosphere appears to 
have been brought at the termination of the carboniferous era, 
and then, and not till then, does it appear that air-breathing 
vertebrated animals were created. Since, then, it has been 
shewn that the identification of strata is a subject of 
great importance to the well-being of man, and that the 
investigation of organic remains is a very essential means of 
identification, and that of all classes of animals the class of 
fishes appears best calculated to aid the labours of the geo- 
logist, more especially in reference to the coal formation, 
it is evident that the study of the fossil Ichthyology of the 
Yorkshire coal-field is appropriate to the business of this 
Society. And from these considerations I was induced, when 
invited by Professor Johnston, a short time ago, to prepare 
a paper for the present meeting, to select this subject, con- 
sidering that a statement even of the little we know of the 
fossil fishes of the district, combined with some general 
observations on the class of fishes, and a brief exposition of the 
classification of M. Agassiz, might form a convenient starting 
point in the study of the fossil Ichthyology of the Yorkshire 
coal-field. IVIr. Teale then proceeded to explain and illustrate 
by specimens from the Museum the Cuvierian classifica- 
tion of fishes, which, from its being based upon the osseous 
system, was shewn to be inapplicable to the purposes of fossil 
Ichthyology,on account of the perishable nature of the bones 
of fishes. Hence it became necessary for M. Agassiz, on 
entering upon the investigation of this extensive and diffi- 
cult subject, to select some other part of their structure, 
less perishable than the bones, as a basis of classification. 
The dermal system, or skin, appeared to Mm the best adapted 
to the purpose, from the imperishable character of the 
scales, and from the scaly integument of fishes not only 
bearing a special reference to the watery medium they 
inhabit, and to the conditions under which they exist, but 
also from its being an index to their internal structure. 
From the form or structure of the scales, M. Agassiz arran- 
ges fishes under four orders, but since two only of these 
existed during the carboniferous era, the author limited 
his observations to the description and geological distribu- 
