Nature of the Imperfection—Questions as to its arising from Want of Continuity, from Lack of Preservation, from Imperfect Collecting.—Examples—Land Snails, Carboniferous Batrachians, Palæozoic Sponges, Pleistocene Shells, Devonian and Carboniferous Plants—Comparative Perfection in the Case of Marine Shells, etc.—Possible Cambrian Squids—Questions as to Want of First Chapters of the Record—Practical Conclusions
Cambro-Silurian Sponges restored.—Protospongia, Acanthodictya, Cyathospongia, Lasiothrix, Halichondrites, Palæosaccus, etc., from a single bed of shale in the Quebec Group, Little Metis, Canada ([p. 47]).
[CHAPTER III.]
THE IMPERFECTION OF THE GEOLOGICAL RECORD.
C
Complaints of the imperfection of the geological record are rife among those biologists who expect to find continuous series of fossils representing the gradual transmutation of species. No doubt these gaps are in some cases portentous, and unfortunately they often occur just where it is most essential to certain general conclusions that they should be filled up. Instead, however, of making vague lamentations on the subject, it is well to inquire to what causes these gaps may be due, to what extent they invalidate the completeness of geological history for scientific purposes, and how they may best be filled.