196 THE JOURNAL OF GEOLOGY. 



the words: "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 recog- 

 nized ; then its series fail and finally its systems and its groups." 



If we accept the correctness of this statement, it is evident 

 that geological terranes and the stratigraphical division -planes 

 by which they are marked, although indicative of time succes- 

 sion, present nothing in themselves to indicate the particular 

 place they occupy in a time -scale. Even were the age of a par- 

 ticular stratum in one section accurately determined by other 

 means, there is no stratigraphical or lithological mark upon the 

 rock stratum, by which the corresponding age can be recognized 

 in another section. This is not meant to imply that it is impos- 

 sible to trace a stratum or formation from one section to another 

 in the same general geological province, for in such case it is a pro- 

 cess of tracing with slight interruption the continuity of the one 

 terrane. But when we pass from one basin to another, the physical 

 continuity is broken, and the stratigraphy and lithology were 

 made on a separate basis. Hence we reach the conclusion that 

 the perfecting of the geological time -scale must be wrought by 

 the means, primarily, of organic remains. Chronological time- 

 periods in geology are not only recognized by means of the fos- 

 sil remains preserved in the strata, but it is to them chiefly that 

 we must look for the determination and classification of the 

 rocks on a time basis. 



This principle is clearly enunciated in the rules adopted by 

 the United States Geological Survey for the direction of the sur- 

 vey.^ "Among the clastic rocks there shall be recognized two 

 classes or divisions, viz: structural divisions and time divisions." 

 "The structural divisions shall be the units of cartography and 

 shall be designated formatiom. Their discriminations shall be 

 based upon the local sequence of rocks, lines of separation being 

 drawn at points in the stratigraphic column where lithologic char- 



' Report of the Director for the Tenth Annual Report, 1890, pp. 63-65. 



