OSCILLATORY CHARACTER OF CONTINENTAL SEAS OO / 



"denote closed or stagnant arms of the sea . . . as in the Black Sea of 

 Eussia" (Schuchert^*). I am inclined to question, more especially the 

 later quoted interpretations, on the grounds (1) that these deposits are 

 usually very widely distributed, (2) that black shale faunas comprise 

 little else than floating marine organisms often strictly cosmopolitan in 

 habitat and therefore requiring currents to effect their distribution, and 

 (3) that the beds overlap to extinction on the flanks of certain interior 

 areas of uplift without material changes, in character. 



The facts at the basis of the last objection are furnished by the Chat- 

 tanooga shale, which pinches out on the very gently sloping surface of 

 the Nashville island of the time and likewise dies out on the southwest- 

 ern side of Ozarkia. Similar conditions were observed concerning other 

 no less typical examples of black shale, like the Utica, or the mucli 

 younger black shale of the Morrow group in Arkansas, Oklahoma, and 

 Missouri. The physical phenomena associated with these overlapping 

 shales establish beyond question that, however extensive, the pans in 

 which the shales were laid down were always very shallow, and this fact 

 proves that great depth of water is not a requisite in black shale deposi- 

 tion. The common though local occurrence of thin scams of coal in the 

 Chattanooga, not to mention the greater development of coal in the 

 Pennsylvanian black shales, tends to the same conclusion. 



As to the facts relied on for the first and second objections, they seem 

 to show conclusively that the Paleozoic black shale deposits in America 

 do not indicate either "stagnant" or more than usually "inclosed" bodies 

 of water that might with any show of right be compared with the Black 

 Sea of today. Not one of these black shale depositing seas can be shown 

 to have been more inclosed than the majority of limestone depositing 

 seas which occupied essentially the same areas in preceding and inter- 

 mediate ages. And why they should be characterized in general as denot- 

 ing "stagnant arms of the sea" is not at all clear in the majority of cases. 

 That the Utica was frequently in, and perhaps always maintained, ample 

 communication with the Atlantic is shown by the distribution of its cur- 

 rent borne pelagic species as far west as central Kentucky, beyond which 

 the sea did not extend. Much the same may be said of the Devonian 

 black shales in the middle Appalachian Valley and western New York, 

 the waters and life of which must have invaded from the east and not as 

 Clarke believes from the west. Nor are the facts materially different in 

 the case of the Chattanooga except that these waters evidently invaded 



» J. M. Clarke : N. Y. State Museum Rept, 57, vol. 3, memoir 6, 1903, p. 200. 

 2* Charles Schuchert : Bull. Geological Society pf America, vol. 20, 1910, p. 446. 



