It is well worth our while to try to understand this statement. Our first and most natural inquiry is, What is it that leads scientists to think so? The details of this particular case are not very accessible, and so we are driven to reasoning from analogy from the known methods and constructions employed in this science. We must agree that none of the authorities who report this circumstance can testify as eye-witnesses of this marvellous event: they were not there on the spot when old Mother Earth turned this huge calcareous and silicious pancake. And yet there must be some kind of evidence by which these eminent men have arrived at this conclusion. What kind of evidence can it be? We cannot imagine any physical evidence which could even remotely suggest such an idea. In fact from the universal custom of making the contained fossils the supreme test of the age of a rock deposit, we are perfectly safe in concluding that it is =solely because the fossils occur here in the reverse of the accepted order=, that we have this astounding picture of an immense mountain mass having been put "upside down over an area of 450 square miles." The "older" fossils are evidently here on top, while the "younger" ones are underneath, and of course some explanation must be given of this flat contradiction of the life succession theory. But let us retrace our steps somewhat, and pick up the thread of our argument. We have already found quite serious reason to question the accuracy of this life succession theory: but there is still another way of testing its rationality. If certain fossils are not necessarily older than certain others, it might reasonably be expected that we would now and then find them reversed as to position, i.e., with the "younger" below and the "older" above. Accordingly we have the following very necessary caution from Prof. Nicholson:[25] "It may even be said that in any case where there should appear to be a clear and decisive discordance between the physical and the palaeontological (fossil) evidence as to the age of a given series of beds, it is the former that is to be distrusted rather than the latter." To meet all ordinary cases of this character, where the differences involve only a few formations representing a few "ages" or a few million years, the theory of pioneer "colonies" was invented by Barrande in 1852. But for extreme cases, say where Silurian or Cambrian fossils occur =above= Jurassic, Cretaceous or Tertiary, there is in such a predicament always an anxious search made for faults and displacements; or gigantic "thrust-faults" or "overthrust folds," like the example already quoted from Dana, are described in picturesque language, many miles in extent--inventions which, as I have already suggested of a similar expedient to explain away evidence, deserve to rank with the famous "epicycles" of Ptolemy, and will do so some day. Here is Geikie's highly instructive statement regarding the same conditions:--