300 GEOLOGICAL RELATIONS OF THE ROCK SYSTEMS 



able to prove most clearly and conclusively, from other evidence, the 

 fact of this succession in time. But, however unquestioned this fact 

 may be in one locality, an attempt hastily to apply it to all others would 

 be simply to revert to the false reasoning which, in the earlier history 

 of our Science, so materially impeded its progress. If we seek justly 

 to compare one series with another, we must first ascertain what is 

 actually the succession of the formations in each case. We can then, 

 but not till then, compare these formations one with the other, and can 

 ascertain whether the changes in one locality correspond with those in 

 the other, we may thus have it in our power to establish some common 

 geological horizon, some common date in time, from which we may 

 reason out geological epochs common to both. 



It necessarily follows, from these considerations, that all geological des- 

 criptions of detached districts in a new country must unavoidably be at 

 first deficient in those very links, which by uniting the rocks of these dis- 

 tricts with the acknowledged succession of rock systems in other and well 

 known countries would give a more general interest to the enquiry. 



Further, the laws of distribution of fossil forms of life, so far as these 

 laws are applicable to the countries in which we are working, are not 

 as yet so well known, that we can safely reason from the occurrence of 

 any particular forms, as compared with their occurrence in other lands 

 at opposite sides of the globe, to any sound conclusions as to the positive 

 epoch of the beds in which they may be found. The system of the rock- 

 masses acknowledged in European geology, and the succession in which 

 these have been formed, may be well known, and the applicability of the 

 same general classification to other countries lying comparatively near on 

 the Earth's surface may be well established, but there still exist vast 

 gaps in the evidence, before these results can be safely generalized. We 

 still want a knowledge of the real equivalents of rock masses, before 

 we can form any true conception of the physical geography, and the 

 organic existence of the surface of our planet, viewed as a whole at the 

 various and successive geological epochs. 



