To sum up, therefore, the aprioristic evolutional series of fossils is not a genuine time-scale. The only safe criterion of comparative age is that of stratigraphic superposition, and this is inapplicable outside of limited local areas.[10] The index fossil is a reliable basis for the chronological correlation of beds only in case one is already convinced on other grounds of the actuality of evolution, but for the unbiased inquirer it is destitute of any inherent time-value. In other words, we can no longer be sure that a given formation is old merely because it happens to contain Cambrian fossils, nor that a rock is young merely because it chances to contain Tertiary fossils. Our present classification of rocks according to their fossil contents is purely arbitrary and artificial, being tantamount to nothing more than a mere taxonomical classification of the forms of ancient life on our globe, irrespective of their comparative antiquity. This scheme of classification is, indeed, universally applicable, and places can usually be found in it for new fossiliferous strata, whenever and wherever discovered. Its universal applicability, however, is due not to any prevalent order of invariable sequence among fossiliferous strata, but solely to the fact that the laws of biological taxonomy and ecology are universal laws which transcend spatial and temporal limitation. If a scheme of taxonomy is truly scientific, all forms of life, whether extant or extinct, will fit into it quite readily. [10] “All that geology can prove,” says Huxley, “is local order of succession.” (“Discourses Biological and Geological,” pp. 279-288.) The anomalies of spatial distribution constitute a sixth difficulty for transformistic palæontology. In constructing a phylogeny the most diverse and widely-separated regions are put under tribute to furnish the requisite fossils, no heed being paid to what are now at any rate impassable geographical barriers, not to speak of the climatic and environmental limitations which restrict the migrations of non-cosmopolitan species within the boundaries of narrow habitats. Hypothetical lineages of a modern form of life are frequently constructed from fossil remains found in two or more continents separated from one another by immense distances and vast oceanic expanses. When taxed with failure to plausibleize this procedure, the evolutionist meets the difficulty by hypothecating wholesale and devious migrations to and fro, and by raising up alleged land bridges to accommodate plants and animals in their suppositional migrations from one continent to another, etc.