C.—GEOLOGY. 99 
in the case of the Corals, Trilobites, and Graptolites. The true relation- 
ship existing between individual fossils and fossil-groups will probably 
only become manifest after searching examination in the field, and 
whilst many of the species previously established will no doubt stand, 
others will probably be found to be more truly related to certain central 
forms as space or time variants (mutations), and may or may not be 
worth specific rank. So that the evolutional work that is required 
must be carried out primarily in the field, though supplementary work 
will have to be carried out in the museum or laboratory ; but the value 
of different features can, I believe, be only truly estimated when they 
are seen making their first appearance, gradually coming to their acme, 
and then dying away to be replaced by others. Thus we may study 
in the field all the stages between fossil A and fossil B, whose relation- 
ship to A would probably otherwise never have been suspected, so 
different do the two extreme types appear. It was indeed truly said 
by your President three years ago’ ‘that not until we have linked 
species into lineages can we group them into genera, not until we have 
unrayelled the strands by which genus is connected with genus can 
we draw the limits of families, not until that has been accomplished 
can we see how lines of descent diverge or converge so as to warrant the 
establishment of orders.’ This is equally applicable to shallow- and 
deeper-water faunas alike, but the time and space variants are best 
seen in shallow-water faunas, where the variation gradient being spread 
out over thicker deposits is less steep than it is in the deeper-water 
faunas, where it is often so steep that the time-variants tend to become 
absorbed in genera. 
The facts just dealt with concern the more purely biological side of 
the question, but for the geologist there is more in the evolutional 
method of work than this. Bearing in mind that Paleontology fulfils 
one of its chief functions as the handmaid or helper of Stratigraphy, 
we may ask how far evolutional work will accomplish that object. 
The answer is clear and definite. The Lower Paleozoic faunas, as has 
already been stated, are essentially Brachiopod-Trilobite faunas 
together with Corals where the seas were sufficiently clear to permit of 
their growth and development. 
As regards the Corals, the kind of work required is that initiated by 
Vaughan, and most ably extended by Dixon, Carruthers, Stanley Smith, 
and others. Lang?!® has recently performed splendid service in the 
cause of evolutional paleontology in putting forward his Doctrine of 
Trends, and showing how Carboniferous Corals follow what he terms 
Programme Evolution, since coral stocks continually developed along 
parallel lines so that different lineages may go through the same 
sequence of changes. We may hope that some such trends may be dis- 
cernible amongst the corals of Lower Paleozoic age, and Carruthers ** 
has shown us how best to obtain the knowledge we require. In 
11 1920, Bather, F. A. Pres. Address to Section C., Cardiff. 
31923, Lang, W. D. ‘Trends in British Carbonif. Corals.’ Proc. Geol. 
Ass., vol. xxxiv, pt. 2, p. 120. 
#1910, Carruthers, R. G. ‘Evolution of Zaphrentis delanouei.’ Q.J.G.S., 
vol. Ixvi, p. 523, &c. 
