316 E. O. ULRICH REVISION OP THE PALEOZOIC SYSTEMS 



enormous deposits of calcareous matter. But, taking the whole sequence 

 as now worked out, we find that the middle Cambrian was locally pre- 

 ceded in the Appalachian Valley and in the Cordilleran basin by great 

 beds of lower Cambrian limestone. In such areas, then, the essential 

 parts of a "cycle" had been accomplished before the close of the lower 

 Cambrian and another begun with the middle Cambrian. This second 

 cycle also was completed long before the close of the Cambrian in the 

 southern Appalachian Valley, where it began with the Rome sandstone 

 and ended with the first limestones of the Honaker group. The third 

 cycle, poorly indicated in the Appalachian region, but well developed in 

 Missouri, began in the latter region with the Lamotte sandstone and 

 closed with the dolomites and limestones of the Bonneterre and Elvins 

 formations. With the last the Cambrian period, as here defined, also 

 terminated. 



The fourth coordinate cycle has a nearly typical development in north- 

 eastern New York, where it began with the Potsdam sandstone and 

 ended with the Little Falls dolomite. 



Though the stages of these four cycles are developed in a reasonably 

 typical manner in the areas mentioned, they are scarcely recognizable in 

 contemporaneous deposits elsewhere. This seems true of all the cycles, 

 of whatever grade ; and herein lies the greatest of the difficulties encoun- 

 tered in applying the criteria of cycles of sedimentation to stratigraphic 

 taxonomy. The point is especially well illustrated by the fourth cycle, 

 which, as said, is satisfactorily expressed in New York, but not even sug- 

 gested by the sequence of deposits in the corresponding part of the Knox 

 dolomite. 



The discrimination of the succeeding Paleozoic cycles of similar rank 

 is often much more difficult. A late Ozarkian one is indicated in Mis- 

 souri by the Roubidoux sandstone and the Jefferson City dolomite. Those 

 of the Canadian, however, are all as yet very obscure, and perhaps can 

 not be determined in America except by assuming that the clastic stages 

 are confined to the marginal provinces and the limestone stages to the 

 Appalachian and other interior provinces. Of the Ordovician cycles w(; 

 recognize the first in the Saint Peter- Joachim series in the Mississippi 

 Valley, but the sequence of deposits making up the succeeding series of 

 this system seems nowhere divisible into corresponding distinct cycles of 

 sedimentation. Like the Canadian, they are represented in the Atlantic 

 province almost entirely by shales ; in the Appalachian and other interior 

 provinces by either limestones only or by limestones below and shales 

 above. The Silurian is like the Ordovician, having a fairly typical cycle 

 at its base (comparable to the Saint Peter- Joachim cycle and closing 



