PRINCIPLES OF STRATIGRAPHIC CORRELATIONS 569 



fortunate happenings, since it is to them we owe the fact that formations 

 which are confined, to distinct troughs in one basin are brought into 

 superposition in another basin. Examples of this kind are cited under 

 principle 6. 



(19) Atlantic invasions occasionally superseded without break by Gulf 

 of Mexico invasions. — Submergence of continental basins beginning with 

 an Atlantic invasion occasionally passed without apparent break into a 

 stage in which Gulf of Mexico invasion prevailed and in which the Atlan- 

 tic connections were reduced, and finally closed. This condition seems 

 to have been brought about by simple tilting, without decided warping of 

 the area concerned. That it obtained is determined by local absence of a 

 stratigraphic break between a fauna of the Atlantic type and a succeed- 

 ing fauna of the Gulf facies. Closure of Atlantic connections was some- 

 times preceded by intermingling of faunas in the Appalachian troughs. 

 The proposition may be illustrated by three examples as follows : 



The stratigraphic relations of the Lowville to the underlying Ottosee 

 formation in east Tennessee, partly described on page 550, indicates that 

 the Atlantic tilt which prevailed in this region during the deposition of 

 the Ottosee was gradually diminished during this age and the Atlantic 

 communication finally closed by emergence about the time that Lowville 

 sedimentation began in Hancock and Hawkins counties. In the section 

 at Bulls Gap, in Bays Mountain, no break was observed in the Ottosee- 

 Moccasin (Bays sandstone) sequence, and as the series between the base 

 of the Ottosee and the base of the Moccasin is very thick here (at least 

 1,600 feet) it is not improbable that sediraientation continued uninter- 

 ruptedly at this locality to and possibly through the Lowville age. How- 

 ever, to the west of Bays Mountain, which is in the Athens trough, the 

 sedimentary process was clearly broken between the thinner Ottosee rep- 

 resentatives and the succeeding Lowville (see page 557). 



The second example is offered by the shales of the Eden group. Proba- 

 bly all will agree that the true ITtica (the "Utica'^ shales of geologic liter- 

 ature range in age from the pre-Mohawkian N'ormanskill to the post- 

 Trenton facies here referred to) had Atlantic connections. One of these 

 seems to have been by way of the Saint Lawrence, another in the region 

 of Chesapeake Bay. This belief is based primarily on fossil evidence. 

 The Atlantic waters of the time extended westward as far as Cincinnati. 

 If Gulf of Mexico waters also invaded the Ohioan province during a por- 

 tion of this age, as seems probable, they were confined in the Ohio Valley 

 to the west of the Carter axis and farther south to the west of tlie Cin- 

 cinnati axis. The new post-Catheys Gratz shale, found in the lower part 

 of the valley of Kentucky Kiver and on the north flank of the Cincinnati 

 dome, is provisionally determined as early Utica in ago. 



XXXVIII — Bull. Geol. Soc. Am.. Vol. 22. 1010. 



