And yet I am tempted to make some effort in this direction. And since we have now examined the _a priori_ aspects of the question, it remains to test the two above mentioned assumptions by the facts of the rocks. The =second=, indeed, involving as it does a profound supernatural knowledge of the past, and being so positively contrary to all that we know of the modern world as to seem essentially absurd, is yet by its very nature beyond the reach of any tests that we can bring to bear upon it. Hence it remains to test by the facts of the rocks =the assumption that all over the earth the fossils invariably occur in the particular order in which they were first found in a few corners of Western Europe= by the founders of the science. Have we already a sufficiently broad knowledge of the rocks of the world to decide such a question? I think we have. To begin then at the beginning, let us try to find out how we can fix on the rocks which are absolutely the oldest on the globe. We would expect to find a good many patches of them here and there, but there must be some common characteristic by which they may be distinguished wherever found. Of course, when I say "rocks" here I mean fossils, for as has long been agreed upon by geologists, mineral and mechanical characters are of practically no use in determining the age of deposits, and we are here dealing only with life and the order in which it has occurred on the globe. Accordingly our problem is really to find that typical group of fossils which is essentially older than all dissimilar groups of fossils.