But before going into the minute description of any of these cases, we must notice some general statements. Thus as long ago as the date of the publication of "The Origin of Species," Darwin, in speaking of the "Imperfection of the Geological Record," could speak of "The many cases on record of a formation conformably covered, after an immense interval of time, by another and later formation, without the underlying bed having suffered in the interval by any wear and tear."[20] Also Geikie,[21] in speaking of how "fossil evidence may be made to prove the existence of gaps which are not otherwise apparent," says that "It is not so easy to give a satisfactory account of those which occur where the strata are strictly conformable, and where no evidence can be observed of any considerable change of physical conditions at the time of deposit. A group of quite conformable strata having the same general lithological characters throughout, may be marked by a great discrepance between the fossils of the upper and the lower part." In many cases he says these conditions are "not merely local, but persistent over wide areas.... They occur abundantly among the European Palaeozoic and Secondary rocks," and are "traceable over wide regions." We have seen how Dana admits that "A stratum of one era may rest upon any stratum in the whole series below it, ... the intermediate being wanting." He classes this under the head of the "=Difficulties=" of the science, quite naturally as it would seem, though he does not expressly assert that these age-separated formations are often =conformable= to one another, as Geikie and Darwin have said in the above given quotations. The literature really teems with illustrations of these facts, and the more detailed accounts contained in the various Geological Reports are often quite charmingly _naive_ in their description of the conditions. Two examples, however, must suffice, both from the Canadian North West. The first is from the Report on the region about Banff, in Alberta, near the line of the Canadian Pacific Railway, and just east of the Rockies. "East of the main divide the Lower Carboniferous is overlaid in places by beds of Lower Cretaceous age, and here again, although the two formations differ so widely in respect to age, one overlies the other without any perceptible break, and the separation of one from the other is rendered more difficult by the fact that the upper beds of the Carboniferous =are lithologically almost precisely like those of the Cretaceous (above them.) Were it not for fossil evidence, one would naturally suppose that a single formation was being dealt with.="[22] The other example is from the District of Athabasca.