478 E. O. IJLRICH REVISION OF THE PALEOZOIC SYSTEMS 



It is not that the rocks do not change in lithic character along the strike, 

 for they do, and sometimes very greatly. The fault lies in the general, 

 more particularly in the indiscriminate, application of the principle. 

 That deposits within and near the littoral zone must be appreciably dif- 

 ferent in quantity or quality or in both respects from sediments farther 

 out is too obvious to require demonstration. But that the change is neces- 

 sarily considerable or even approximately equal in different but corre- 

 sponding parts of a basin is not true. The change in character and vol- 

 ume of the deposits depends on so many variant factors that it is im- 

 possible to frame rules that will be generally applicable and of practical 

 value to the student. Any difference in the altitude, composition, and 

 drainage of adjacent lands and in the climatic conditions prevailing 

 thereon must have exerted some either local or general effect on the char- 

 acter of the marine deposits of the time. (See pages 454 and 467 for 

 further remarks. ) 



Shoreward change in lithic character of formations has been assumed, 

 generally without argument, or as a self-evident principle, by nearly all 

 authors who have sought to account for, more particularly the observed 

 east-west variations in Appalachian Valley deposits, which they regarded 

 as synchronous. N^evertheless it seems to be a fact that unquestionable 

 occurrences of this kind are really exceptional and certainly not very 

 common. As a rule the presumed lithically changing stratigraphic zones 

 have proved to comprise deposits that were laid down not only at different 

 times but in distinct troughs. For instance, the Knox dolomite in east 

 Tennessee was thought to lose its chert in passing from the west to the 

 east side of the valley. In fact, however, the supposed eastern repre- 

 sentative is a later deposit that in turn fails to extend westward across 

 the valley. Similarly the great Chickamauga limestone series of tlie 

 western side of the valley was thought to change so that at the eastern 

 edge the limestone gave way almost entirely to shale and sandstone. Wc; 

 know now that this is untrue, and that instead of synchronous, laterally 

 changing deposits, the Ordovician rocks of the valley were laid down at 

 varying times in several distinct, though now more or less overthrust, 

 troughs, to each of which certain stratigraphic units, differing litho- 

 logically, faunally, and chronologically from the rest, are confined. 



As is to be expected, decided lateral change in lithic character of strati- 

 graphic zones is even more exceptional in the interior basins of North 

 America than in the Appalachian troughs. In these also the supposed 

 local variations are usually found to pertain to beds of different and not 

 the same ages, or if not that then to deposits in distinct geological prov- 



