&58 G. K. Gilbert — Congress of Geologists. 



From this point of view a system is somewhat artificial, but 

 there is a more important sense in which it is natural. It is 

 limited by stratigraphic or paleontologic breaks above and be- 

 low, and these breaks are natural. The taxonomist is not war- 

 ranted in dividing systems where no such break exists. 



Transferring now our attention to some other area, distant 

 from the first, and studying its stratigraphy, we find that the 

 same principles enable us to divide it independently into stages, 

 series, systems and groups. Its fossils are not the same, but 

 they are to a certain extent similar, and the sequence of life is 

 approximately parallel. We cannot compare stage with stage, 

 nor series with series perhaps, but we can compare system with 

 system, and making the comparison we discover that the breaks 

 are at different places. While one area was upraised and sub- 

 jected for a time to erosion, the other received continuous de- 

 position. While life in one area, enjoying constant conditions, 

 was almost unchanged for long ages and even epochs, it was 

 revolutionized in the other by the irruption across some obso- 

 lescent barrier of strong and aggressive faunas and floras. The 

 systems of one area, therefore, do not coincide with the sys 

 terns of the other in their beginning and ending. They may 

 differ in number, and they may differ greatly in magnitude and 

 in the duration they represent. They are in fact a different set 

 of systems. 



The case I have described is ideal but not false. It represents 

 the common experience of those who have developed the geolog- 

 ic histories of remote districts and attempted to correlate them 

 with the geologic history of Europe. There does not exist a 

 world-wide system nor a world-wide group, but every system 

 and every group is local. The classification developed in one 

 place is perfectly applicable only there. At a short distance away 

 some of its beds disappear and others are introduced ; farther 

 on its stages cannot be recognized ; then its series fail and finally 

 its systems and its groups. 



If I have properly characterized stratigraphic systems — if 

 they are both natural and local — it goes without saying that the 

 classification of the strata of all countries in a dozen or so sys- 

 tems, as proposed by some of the members of the congress, is 

 impossible. 



I hasten to add that from the point of view of these gentle- 

 men what they advocate is not necessarily impossible, for they 

 have a different conception of a system. They regard it not as 

 local but as universal. It is their privilege to define their terms 

 as they please, and we will not dispute about mere words, but I 

 cannot too strongly or too earnestly insist that a system which 

 is universal is artificial. It may be natural in one geologic 

 province, but it is artificial in all others. Take for example the 



