436 G. K. Gilbert— Congress of Geologists. 



of work on the map of Europe pressed the congress for the de- 

 termination of questions on which hung the completion of the 

 map, and many hasty decisions were reached, while not a few 

 disputed points were referred to the map committee. The debates 

 indicate that much or all of this work was provisional or of 

 merely local application, but the resolutions adopted show lit- 

 tle qualification. It should be added that the official minutes 

 of the meeting are still unpublished. In view of the uncer- 

 tainty thus occasioned I shall not attempt to characterize the 

 attitude of the congress on the subject of classification, but 

 shall merely develop my individual view. 



It is the opinion of many who have discussed the general 

 classification of terranes by convention of geologists that the 

 smallest unit of such classification should be the stratigraphic 

 system. What is a stratigraphic system ? The congress im- 

 plies a definition in saying that a system includes more than a 

 series and less than a group, and that the Jurassic is a system ; 

 but this gives only a meagre conception and we need a full one. 

 As the problem of classification demands a true conception of 

 a system, and as there is reason to believe that a false concep- 

 tion is abroad, it is proper that in seeking the true one we begin 

 with the elements. 



The surface of the land is constantly degraded by erosion, 

 and the material removed is spread on the floor of the ocean, 

 forming a deposit. This process has gone on from the dawn of 

 geologic history, but the positions and boundaries of land and 

 ocean have not remained the same. Crust movements have 

 caused the submergence of land, and the emergence of ocean 

 bottom, and these movements have been local and irregular, 

 districts here and there going up while other districts went 

 down. The emergence of ocean bottom exposes the deposit 

 previously made on it and subjects it to erosion. In this way 

 every part of the known surface of the globe has been the scene 

 of successive deposition and erosion, and in many districts the 

 alternations of process have been numerous. It is manifestly 

 impossible that either erosion or deposition should have ever 

 prevailed universally, and it has been established by the study' 

 of stratigraphic breaks that a time of erosion has often inter- 

 rupted deposition iu one region while deposition was uninter- 

 rupted in another. 



In transportation from its region of erosion to its place of 

 deposition detritus is assorted, and it results that the simultane- 

 ous deposits on the bottom of an ocean are not everywhere the 

 same. Equal diversity is shown in the ancient deposits consti- 

 tuting geologic formations. It is a general fact that syn- 

 chronous formations have not everywhere the same constitution. 



Many of the variations in deposits are correlated with depth 



