120 Anniversary Address to the 
nomena to be accounted for, and which as yet have not been 
referred to any law that I know of. 
For some years I have livedin hope of the discovery of a pale- 
ozoic fauna and flora more in accordance with those of after 
epochs than those we know, and fondly fancied that local 
differences of physical conditions alone might account for the 
discordance. But the fields opened by Murchison, Sedgwick, 
and Phillips, have been so extended, and have yielded such 
rich harvests at the hands of James Hall and his fellow-ex- 
plorers in America, and of Barrande, de Koninck, de Verneuil, 
the Rémers and Sandbergers, M‘Coy, King, Salter, Roualt, 
and many other able paleontologists who have worked at pa- 
leozoic fossils in Europe, that it is becoming evident that we 
have before us a fair and true image of at least the marine 
aspect of the primeval group of faunas. ‘The more they are 
investigated, the wider the ground is explored, the more 
striking is the difference in the main between the life pa- 
Ieozoic and the after-life. 
Doubtless a principal element of this difference lies in sub- 
stitution—in the replacement of one group by another, serv- 
ing the same purpose in the world’s economy. Paradoxical 
must be the mind of the man, a mind without eyes, who in 
the present state of research would deny the limitation of 
natural groups to greater or less, but in the main continuous, 
areas or sections of geological time. Now, that greater and 
lesser groups—genera, subgenera, families, and orders, as 
the case may be—or, in truer words, genera, of different 
grades of extent—have replaced others of similar value, and 
served the same purpose, or played the same part, is so evi- 
dent to every naturalist acquainted with the geological dis- 
tribution of animals and plants, that to quote instances would 
be waste of words. This replacement is substitution of group 
for group—a phenomenon strikingly conspicuous on a grand 
scale, when we contrast the paleozoic with the after faunas 
and floras. A single instance of these greater substitutions 
may be cited to assist my argument, viz., the substitution of 
the Lamellibranchiata of later epochs by the Palliobranchiata 
during the earlier. In this, as in numerous other instances, 
ak" & 
