FOSSIL PEDIGREES 101 



anything analogous to our present-day geographical distribu- 

 tion of plants and animals into various biological provinces, or 

 be prepared to show by what infallible criterion we are enabled 

 to distinguish between synchronously deposited formations 

 indicative of a geographical distribution according to regional 

 diversity, and consecutively deposited formations indicative of 

 comparative antiquity. 



The former alternative does not merit any consideration 

 whatever. The latter, as we shall presently see, involves us in 

 an assumption, for which no defense either aprioristic or factual 

 is available. We can, indeed, distinguish between spatial, and 

 temporal, distribution within the narrow limits of a single 

 locality by using the criterion of superposition; for in regions 

 of outcrop, where one sedimentary rock overlies another, the 

 obvious presumption is that the upper rock was deposited 

 at a later date than the lower rock. But the criterion of 

 superposition is not available for the correlation of strata in 

 localities so distant from each other that no physical evidence 

 of stratigraphic continuity is discernible. Moreover the in- 

 duction, which projects any local order of stratigraphical 

 sequence into far distant localities on the sole basis of fossil 

 taxonomy, is logically unsound and leads to conclusions at 

 variance with the actual facts. Hence the alleged time-value 

 of index fossils becomes essentially problematic, and affords 

 no basis whatever for scientific certainty. 



As previously stated, the sequence of strata is visible only in 

 regions of outcrop, and nowhere are we able to see more than 

 mere parts of two or, at most, three systems associated to- 

 gether in a single locality. Moreover, each set of beds is of 

 limited areal extent, and the limits are frequently visible to 

 the eye of the observer. In any case, their visible extent is 

 necessarily limited. It is impossible, therefore, to correlate the 

 strata of one continent with those of another continent by 

 tracing stratigraphic continuity. Hence, in comparing parti- 

 cular horizons of various ages and in distinguishing them from 

 other horizons over large areas, we are obliged to sub- 



