394 E. O. ULRICII REVISION OF THE PALEOZOIC SYSTEMS 



instance, the Bigby Trenton or the Maquoketa Richmondian, the minoi- 

 term being given the qualities of an adjective. Or it may be desirable 

 to refer to the time of the Bigby, which term, having perhaps not yet 

 attained general recognition, exactitude of expression might be secured 

 by writing Bightj Trenton. Finally, in discussing thick formations in 

 which one or more ages is recognized, these ages or parts might be re- 

 ferred to as the Trenton Chickamauga, the LowviUe Chambersburg, the 

 Pamelia Stones River, the Rochester Clinton, the Onondaga Romney, 

 etcetera. Often, too, one may insure exact and immediate understand- 

 ing of time significance of local terms by using an expression like "the 

 middle Trenton Bigby limestone." 



PART II. CRITERIA AND PRINCIPLES OF STRATIGRAPHIC 

 CLASSIFICATION 



DiASTROPHic Criteria 



BODY DEFORMATION CAUSING VERTICAL MOVEMENT OF LAND AND 

 SHIFTING OF CONTINENTAL SEAS 



General discussion and permanence of oceanic basins. — An adequate 

 discussion of the criteria and principles of diastrophic correlation 

 would fill a volume — and doubtless the effort would be worth while. 

 But on account of lack of space summary treatment, confined as much 

 as possible to the practical aspects of the main purpose of this work, 

 must suffice for the present. It is to be said, however, that much of the 

 matter to be presented under the heads "gradational and lithological 

 criteria" (pages 467 to 480) and "correlation by lithological similarity" 

 (pages 519 to 532), also in several chapters of Part I, is really a discus- 

 sion and application of diastrophic criteria. Even the organic criteria 

 are, to a large extent, expressions of diastrophic activity. 



For purposes of stratigraphic correlation and classification the pri- 

 mary cause or causes of diastrophic movements — especially those result- 

 ing in coij^iderable horizontal shortening — are not of vital importance. 

 We are here concerned chiefly with the fact that such movements have 

 taken place and with the determination of the general nature of their 

 effects on agencies at work on the surface of the earth. It will be agreed 

 by most of us that such deformation had a fundamental bearing on the 

 migration of the strandline and on the relative elevation or depression 

 of parts of the surface, hence on the extent of marine deposition and the 

 character of the deposits. It also affected the evolution and distribution 

 of faunas. 



