360 E. O. ULRICH REVISION OF THE PALEOZOIC SYSTEMS 



suggested itself that their origin is in some manner connected with cool 

 temperatures. It is not that glacial climates prevailed at such time, but 

 only that the average, or at least occasional, temperature on the lands 

 adjacent to the continental seas was too low to encourage the develop- 

 ment of normal littoral faunas. In other words that the climates pre- 

 vailing at times and places of black shale deposition in continental seas 

 were cool enough to render their shores inhospitable to contemporaneous 

 littoral and benthonic life. Decidedly frigid conditions may have ob- 

 tained occasionally or locally during such times but they are not essential 

 to the proposition. 



Various other facts might be cited in support of the suggested relation 

 of black shale deposition to cool climate. Thus black shales occur in 

 greatest abundance in submarginal regions. All agree that these were 

 frequently elevated to considerable altitudes, a condition doubtless tending 

 to lower the average temperature of adjacent land seas. In the more 

 interior areas black shales were formed chiefly toward, or soon after, the 

 close of periods (the Utica, the Genesee, the Chattanooga, and the 

 Fayetteville), or near the close of epochs (the Caney-Morrow), hence 

 when local highly emergent conditions, presumably favoring diversity 

 of climates, commonly prevailed. Migration of littoral and benthonic 

 faunas from the oceanic basins (on which cold temperatures prevailing 

 on adjacent lands would have had comparatively little effect) into the 

 continental troughs and basins must under such conditions have been 

 very limited and perhaps were soon stopped entirely. Only the current 

 borne pelagic forms, which are much less affected by unfavorable shore 

 conditions, could have entered and existed in the interior basins. The 

 very slight amount of calcareous matter in black shales also is suggestive 

 of cool rather than, warm climates. This is inferred from the fact that 

 all classes of marine invertebrates, especially reef corals and associated 

 bryozoa, on which warm waters are confidently postulated by paleontol- 

 ogists, are wholly absent in black shales and almost confined to calcareous 

 deposits. 



The Pennsylvanian black shales, considering that until recently this 

 period has been universally regarded as favored by an unusual extension 

 of warm climates, may suggest an exception. But I am not at all con- 

 vinced that this period was especially warm. The prevalence of clastic 

 sedimentation indicates contributing lands of considerable altitude, which 

 should have tempered the climate. Peat deposits are being formed today 

 mainly in northern regions ; and 30 to 40 feet of coal are included in the 

 Permo-Carboniferous glacial deposits in Australia. Further, the Caney 



