ANNIVERSARY ADDRESS OE THE PRESIDENT. 213 



with the vegetation of the Carboniferous epoch, and, with other 

 remains in the same rocks, show that the Atlantic ocean covers a 

 vast area of once continuous or contiguous land. 



Every one who has studied the varied conditions of the Carbo- 

 niferous series, the deposition of its strata, the distribution of its 

 fauna, will at once admit that its history is only to be written 

 through the great and reliable group of the Mollusea (Brachiopoda, 

 Lamellibranchiata, Gasteropoda, Pteropoda, Heteropoda, and Cepha- 

 lopoda), whose 6 divisions or classes number 116 genera and 1020 

 species, or nearly one half the entire known Carboniferous fauna. So 

 many of the genera have come down to the present day, that infe- 

 .rentially, through observation, we know their habits in Carboniferous 

 times ; they show us that, during or throughout the accumulation 

 of the Carboniferous Limestone, moderately deep-sea conditions 

 prevailed, and the Molluscan fauna then surpassed all subsequent 

 numerical development during the Carboniferous period. Ultimately 

 physical changes caused the sea to shallow, thus altering all bathy- 

 metrical conditions at the same time : littoral species died out, 

 through altered circumstances ; and the habits of the deeper-sea 

 fauna changed also on slow elevation, the zonal lines of life under- 

 going modification through adaptation. Plainly are these modifi- 

 cations and changes to be observed through the several stages, from 

 the Calciferous Sandstones to the summit of the Coal-measures. 

 Zoologically, only the last five stages of the Carboniferous group 

 have to be considered, as so great a change took place at the close of 

 the Gannister group or Lower Coal-measures, the succeeding beds 

 illustrating terrestrial conditions through the rich and earliest exten- 

 sive flora known (vide Table at end of Carboniferous system, p. 226). 

 No one has felt the difficulty of showing the distribution of life 

 through the Carboniferous group more than myself, the rich fauna 

 that characterizes the series from the Calciferous Sandstones to the 

 top of the Gannister (or Lower Coal-measure) beds being most diffi- 

 cult of analysis. 



Every extended sea-bed has its own conditions and its own fauna ; 

 the exact nature of that sea-bottom it is difficult to predicate ; it 

 can only be learnt through examination. Admitting that the fauna 

 of any group of rocks is, or was, as local as the physical condi- 

 tions during deposition, and the maximum of life is usually local, 

 it will show itself in any area, in any part of an epoch or of a 

 stage; it is governed chiefly by the nature of the sediment and 

 by temperature. The questions of appearance of species, duration, 

 migration, extinction, recurrence, and many other conditions that 

 govern marine life in all its phases are to be studied through a 

 careful investigation of the physical history of the Carboniferous 

 rocks ; and through no other zoological group do we receive so much 

 instruction as through the Mollusea. 



Brachiopoda. — Both the Tretenterata, or " Inarticulata," and the 

 Clistenterata, or " Articulata," are largely represented in the Carbo- 

 niferous rocks ; and many genera appear for the first time, and 



VOL. XXXVII. q 



