498 STUDIES POR STUDENTS 
on the title-page, and the sixth 1829, a work in which very many 
of the species of British fossils were originally described, may be 
taken as a type of this group of works. In the arrangement of 
the matter included in these volumes no attempt is made at 
classification, either zodlogically or according to the geologic 
horizons in which the fossils were found. It is simply a paleon- 
tologic scrapbook, as it were, of descriptions and illustrations of 
fossil species. One plate, with its accompanying descriptions, 
may be devoted to Tertiary gastropods, the next to Paleozoic 
brachiopods, a third to Cretaceous ammonites, a fourth to Ter- 
tiary gastropods again, and so on, the total number of plates in 
the whole work being 648. 
Following the early period in which there was to a great 
extent an absence of classification, the classification of fossils 
gradually developed along two distinct lines. On the one hand, 
with the increase of knowledge and with the progress in taxon- 
omy of living organisms, the zodlogical classification of fossils 
made rapid strides, and many orders, families and genera founded 
wholly upon fossil forms were established, and were fitted into 
the scheme of classification of all organisms, making it far more 
complete than it could ever have been made from the study of 
living organisms alone. On the other hand, there grew up a clas- 
sification of fossils into faunas, so that a whole series of extinct 
faunas, from the earliest Paleozoic time to the recent, were recog- 
nized. It also gradually came to be established that the sequence 
in time of extinct faunas, in their larger characteristics, was the 
same for all parts of the world where fossils were found. 
For many years these two systems of classification of fos- 
sils went forward hand in hand, but with the development of 
the science the two paths along which progress was being 
made became more and more divergent, until at the present 
time the two divisions of the subject have become fully differ- 
entiated. 
It is of interest to trace the differentiation of these two lines 
of progress in the life work of such a paleontologist as the late 
James Hall, whose career extended over more than half a century. 
