NEW GEOLOGIC TIME TABLE 603 



recognized, form the only true basis for a delimitation of chronological 

 periods." 266 Diastrophism as determined by the successive faunas and 

 their plotting on paleogeographic maps seems to include the physical 

 principle that will not only render the formations of a province capable 

 of being grouped into periods, but will serve as a fairly reliable guide for 

 intercontinental correlations of like and unlike faunas as well. If the 

 principles of diastrophism and paleogeography are to be made the basis 

 for the future delimitation of periods or systems, the personal equation 

 of workers in regard to the period value to be given this or that fossil or 

 fauna is reduced to a minimum. In such a classification the disposition 

 of a newly discovered horizon will adjust itself automatically on the basis 

 of its paleogeography. If such maps can not be made, however, and the 

 local conditions are not final, then temporary adjustment must of course 

 be based on faunal affinity. 



With these principles as a basis, the curve chart (plate 101) has been 

 constructed, and from it may be seen that since the beginning of Paleo- 

 zoic time there have been at least 17 inundations, and that these are 

 separated from one another by an equal number of high nodal points or 

 emergent periods. On the chart, therefore, a period or system embraces 

 the time represented by the space between two high nodes of the curves, 

 including one more or less long low, or inundation. This method has 

 been used by the writer 267 since 1902, when he stated that "each system 

 should begin with a subsidence and end with an emergence." 



According to the geological text book of Chamberlin and Salisbury, 

 the geologic column has 13 systems, if the Tertiary is divided into two 

 periods, as is now generally the practice. From the chart herewith pre- 

 sented it is learned that there are 17 submergences, or lows, and it would 

 seem, therefore, that the inherited classification is not borne out by the 

 newer principles of paleogeography and diastrophism. A closer analysis 

 of these curves, however, brings out the fact that in general the eras have 

 hitherto been correctly defined, but that in detail the periods must be 

 newly delimited in a number of places. The most marked of these 

 changes is the division of the Cambrian and Ordovician each into three 

 periods and the Mississippian into two periods. The bases for these 

 major changes are described elsewhere in this work, while the new delim- 

 itation of the old periods is indicated at the top of the chart. 



Of less importance are the following results : On the sole basis of the 

 diastrophic curve for the "United States," it is still debatable whether 



Antlitz der Erde, vol. 1, 1883 ; Sollas translation, vol. 1, p. 14. 



Ulrich and Schuchert : Report of the New York Paleontologist, 1902, p. 659. 



