Devonian Shales of Northern Ohio. 195 



Andrussow* Lave deep significance in connection with the 

 interpretation of the marine conditions which produced the 

 diverse faunas and stratigraphy of the Ohio shale. Their 

 interest in this connection suggests the introduction here of a 

 portion of Clarke'sf quotation of Pompeckj's;}: observations on 

 the Black sea: 



"The sediments of the black sea are: (1) in the littoral zone 

 and to a depth of about 20 fathoms, accumulations of sandy 

 detritus ; (2) to the 100 fathom line, gray blue sticky mud, from 

 35-100 fathoms, rich in Modiola phaseolina, etc. ; (3) in the great 

 depths the bottom is covered with (a) very fine, sticky, black 

 mud with rich separation of FeS, abundant remains of planktonic 

 diatoms and with fragments of quite young lamellibranchs (early 

 stages of widely scattered plankton forms, (b) dark blue mud ; 

 FeS is here in less measure, but in richer quantity are separations 

 of minutely grained CaC0 3 , making at times thin banks ; skeletons 

 of pelagic diatoms are also abundant." 



From these observations it appears that the Black sea 

 furnishes an example of black sediments now forming in its 

 deeper parts which are essentially like those of the Cleveland 

 and Huron shales. The accumulations of sandy detritus in the 

 more shallow parts of the same sea represents a type of 

 deposits similar to the Chagrin shale. 



We pass now to a brief consideration of the second class of 

 evidence on which the overlap theory rests, namely, the present 

 relative attitude of the dark shales and the underlying lime- 

 stone. The Cleveland shale and the Devonian limestone at the 

 base of the shale series show a gentle dip in opposite directions, 

 the latter toward the Allegheny region, the former away from 

 it The interpretation placed by Ulrich on the diverse declina- 

 tions of the Cleveland shale and the Devonian limestone is 

 that the former represents a marine basin entirely distinct from 

 the one in which the shale following the Devonian limestone in 

 eastern Ohio was laid down. Opposed to this interpretation, 

 however, there is a well established and universally accepted 

 fact. If there is any general fact regarding the Devonian 

 shales which is better attested than others in eastern Ohio, it 

 is the rapid thickening of the series in passing eastward toward 

 the Allegheny region. Hence, it follows that unless the east- 

 erly declination of the basal floor of Devonian limestone is 

 more rapid than the rate of thickening of the shales, the con- 



* La Iter Noire : Guide des excursions du 7 Congres geolog. internat. 

 1897, No. 29. 



f Clarke, John M. : Naples fauna in western New York, New York State 

 Mus. Mem., vi, p. 201. 1904. 



:{: Porupeckj : Die Jura-Ablagerungen zw. Eegenstrarg und Eegenstauf 

 (Separate from Geognost. Jahresheft. 1901, 14 Jahrgang, p. 43 et seq.) 



