Geological Distribution of the Rhabdophora. 449 
the mouth-organs and eyes, showed the same structure, in 
equal definiteness and perfection, as the larger castes. Allu¬ 
sion was also made to the ravages of these destructive insects ; 
and some of the modes for exterminating them were ex¬ 
plained. 
XLIX.— On the Geological Distribution of the Rhabdophora. 
By Charles Lapworth, F.G.S. 
Part I. Historical. 
[Continued from p. 257.J 
(d) Recent Research. 
Geological. —It has been already shown that those geologists 
whose leanings were mainly palaaontological accepted without 
question the reference of all prolific Graptolite-bearing strata to 
the general horizon of the Llandeilo formation, and endeavoured 
to escape from the numerous difficulties in which they conse¬ 
quently found themselves involved by appeals to the recog¬ 
nized rule of the restriction of certain fossil groups to special 
sediments, by references to the phenomenon of migration, by 
the adoption of the theory of “ Colonies,” and the like. But 
there were, in addition, a few influential geologists who 
looked upon geology almost wholly from the physical side, 
and who naturally relied only upon such paleontological testi¬ 
mony as distinctly coincided with the inferences they drew 
from the stratigraphical evidences. These viewed all attempts 
to correlate strata of disconnected areas by means of the 
Rhabdophora with the gravest suspicion, passing over with a 
careless indifference the clearest indications of a natural suc¬ 
cession afforded by those entered upon their fossil lists. When, 
as occasionally happened, the palaeontological testimony af¬ 
forded by these fossils conflicted with that drawn from the 
apparent physical evidences, no matter how scanty or ambi¬ 
guous, they at once set it aside with undisguised contempt. 
However mortifying it may be to the graptolithologist to 
admit the fact, it cannot be denied that this course was at all 
events quite as reasonable as the habit of the over-credulous 
majority. The cautious field-geologist, on consulting the 
works of those who had made these fossils the subjects of 
special study, learnt at once that, according to the best autho¬ 
rities, many of the most characteristic Llandeilo Graptolites of 
Britain occurred in America in the very highest beds of the 
