364 E. O. ULRICH REVISION OF THE PALEOZOIC SYSTEMS 



in old fissures and caverns which had been excavated in the underlying 

 rock during a preceding period of emergence. Such cases, however, are 

 more commonly explained by assuming sedimentation and subsequent 

 removal of the deposit by erosion except where it lodged in the protecting 

 fissures and caverns. Though as a rule disinclined to adm^it considerable 

 degradation in "negative" areas, this explanation can not always be 

 successfully denied. Such a case, for instance, may be the very early 

 Waverlyan deposits containing fish remains of the genus Ptyctodus 

 found in enlarged joint planes in the Niagaran dolomites at Chicago. 

 This region, namely, was subjected to subaerial agencies during a long 

 period, extending from the early Waverlyan to at least the Pennsylvanian 

 and probably to the present time. Another such case may be the rem- 

 nants of Oriskany sandstone at Buffalo, New York. However probable, 

 it may yet be contended that the evidence of blanket erosion is in neither 

 case convincing. Such erosion is much more likely in the case of the 

 remnants of Boone and .Burlington limestone and Pennsylvanian shales 

 deposited in and still filling Paleozoic sinkholes on the Ozark uplift. 



But there are other cases — rare, it is true — of deposits occurring 

 locally only in earlier solution cavities that are most probably not mere 

 remnants of sheets otherwise removed by surface erosion. I have in 

 mind two Ordovician caverns filled with later Ordovician shales that 

 are not represented in the section on either side of the caverns. One 

 of these is found in a railroad cut about 6 miles west of Saint Genevieve, 

 Missouri, the other in a quarry at Darlington, Wisconsin. Being clearly 

 near-shore occurrences, these instances of localized sedimentation suggest 

 shore and tidal currents or wave action, or both, as prohibiting deposition 

 except in depressions of the sea bottom. But, as said, such occurrences 

 are very exceptional in Paleozoic seas. 



There is reason to believe further that conditions favoring non- 

 deposition and even scour occurred in certain submarginal troughs having 

 wide-mouthed connection with permanent oceanic basins and through 

 which large volumes of water may have been poured. Ideal examples 

 of such troughs would be the early Paleozoic channels on the inner 

 border of the marginal lands of the North American continent, like the 

 Levis channel, which connected the Saint Lawrence embayment with 

 the middle Atlantic somewhere near Delaware Bay ; or like the Athens 

 trough or channel, which is believed to have opened at the north into 

 the Atlantic about Chesapeake Bay and at the south into the Mexican 

 sea. Littoral, in fact bottom-dwelling faunas of any sort, scarcely ex- 

 isted in these troughs, the known fossils being almost entirely types 



