366 
paleontologists. It has been hastily assumed by some, Barrande 
himself leading in this respect, that the mental conception was 
more than could be realized in nature; and that the imperfection 
of the recorded succession was an obvious refutation of the doctrine 
of evolution, and all pursuit of a solution unworthy of serious 
attention. 
Statistically, the logical picture coincides with the observed suc- 
cession in time. The straight cones predominate in the Silurian 
and earlier periods; while the loosely coiled are much less numer- 
ous, and the close coiled and involute, though present, are also’ 
rare. The close coiled, or nautilian shells, gain in numbers in the 
Carboniferous, and the involute—meaning by this those that en- 
velop more or less the inner and younger whorls—are much more 
numerous than in the Silurian; while, in the later times of the 
Jura, all disappear except the involute. 
_ But suppose we reverse the course of nature and follow back the 
diminishing number of nautilian and gyroceran shells. We then 
see, upon arriving at the Silurian, that the vanishing point of these 
shells, although not traceable on account of the lost records of 
Protozoic time, could not have been far distant, while the increas- 
ing number and varied forms of the straight cones indicates for 
them a more remote focus in time and consequently a more ancient 
origin. Thus we are able to see, that antecedent to the Silurian, 
in the Protozo:c, there must have been a time when the straight 
cones or their immediate ancestors predominated, to the exclusion 
of the coiled and perhaps even of the arcuate types. 
The involute shells of the earliest geological times were, there- 
fore, probably evolved from the straight cones in regular succession ; 
and we may, perhaps, hope to eventually get the evidence of this 
succession in the fossils themselves. The exact counterpart of our 
logical picture, as Barrande has truly stated, does not, however, 
exist in the known geological records of later periods. Judged by 
the coramon classification, by the prevalent ideas about the affinities 
of adult structures, and by the modes of occurrence of fossils in the 
rocks, the forms seem to be without law or order in their succession, 
and that eminent author’s objections to the theory of evolution 
have never been fairly met and refuted by any modern writer. 
But let us imagine, during the Paleozoic, a different condition of 
affairs from what is now the general rule. Let us suppose such a 
thing possible as the quick evolution of forms and structure, and 
