462 E. O. ULRICH CORRELATION OF THE STRAND-LINE 



original formation. Of course, we long ago began to correct the nu- 

 merous errors that resulted from indiscriminate application of this wrong- 

 principle ; and the longer we work, the more expert we become in detect- 

 ing the weeds that had taken root in our stratigraphical garden. But 

 some of these weeds have grown into lusty eye-filling plants, whose eradi- 

 cation, therefore, is strenuously opposed by those who believe in letting 

 well enough alone and who object to any innovation that means change 

 in prevailing method and practice. 



This old belief and practice made us close our eyes even to patent 

 fauna! differences. A case in point is that of the basal series of the 

 Paleozoic in the Upper Mississippi Valley — a succession of varying sand- 

 stones — which up to very recently was correlated with the Potsdam sand- 

 stone of ISTew York. This identification was made and maintained despite 

 the long known fact that the large faunas of the two series have not a 

 single unquestionably identified species in common. But it is now evi- 

 dent through study of the fauna of the Madison sandstone — an Ozarkian 

 deposit — that the Saint Croixan or Upper Cambrian series of Wisconsin 

 is much older than the Potsdam sandstone, which, with the overlying 

 limestones, makes up the typical Saratogan series of ISTew York. On the 

 other hand, the fauna of the Madison includes peculiar trilobites and 

 gastropods that are unknown elsewhere except in the Potsdam sandstone 

 and the Hoyt limestone of New York. Specifically definite faunal evi- 

 dence thus has finally come to the support of my assignment of the Sara- 

 togan series of New York to the Ozarkian system. It may be of interest 

 to note that the considerations which originally induced the conviction 

 that the typical Saratogan is younger than the top of the Upper Cambrian 

 in the Mississippi Valley, and elsewhere in the central and western parts 

 of the United States, were solely of the diastrophic kind. They were 

 concerned with probabilities of crustal movements rather than faunal 

 data. 



A largely similar case involves the Devonian-Mississippian boundary in 

 eastern North America, This is the disputed general equivalence of the 

 chiefly black Ohio, New Albany, and Chattanooga shales to the Upper 

 Devonian Genesee and Portage shales, on the one hand, and to the Lower 

 Mississippian Kinderhook series on the other. The former relation was 

 asserted before I was born and has been the prevailing view down to the 

 present time. However, in the past 10 years I have repeatedly denied 

 this view, claiming, on the contrary, that the black shales of the Middle 

 Western States are younger than the top of the Devonian in New York, 

 from which region the universally accepted standard for the Devonian 

 system in America is derived. Much new evidence on this problem has 

 been acquired in the past two years. Most of this has been studied, so 



