PRINCIPLES OF STRATIGRAPIIIC CORRELATIONS 527 



Somewhat different cases are certain sandstone and shale deposits which 

 at one point may seem to constitute a single, indivisible lithologic unit, 

 but when traced along the outcrop are seen to divide at some plane be- 

 tween the top and bottom of the bed. Four instances come to mind, two 

 in which the dividing bed is of sandstone and two of shale. The first is 

 the rather well known case of the Glauconite sandstone of the Baltic 

 region, which wedges apart in Sweden so as to inclose the Ceratopyge 

 limestone between an upper and a lower division of a bed that elsewhere 

 has the appearance of an indivisible unit. The second case is more re- 

 markable because the included hiatus is much greater. It was observed 

 at several localities in northern Arkansas and concerns a white quartzose 

 sandstone which on several occasions had been mapped as a unit, but of 

 which, it was found on closer investigation, the lower part is of Saint 

 Peter or earliest Ordovician age, while the upper part is early Waverlyan, 

 being either the Sylamore sandstone member of the Chattanooga forma- 

 tion or a sandstone at the base of some stage of the succeeding Kinderhook 

 overlap. Away from the points where the sandstones unite in a single 

 lithologic ^'"unit" the upper and lower parts diverge until they are sepa- 

 rated by from 500 to 600 feet of Ordovician and Silurian limestone (see 

 figure 17 D, page 450). Without knowledge of these facts one would be 

 likely to refer the combined sandstones to either the Saint Peter or the 

 Sylamore. These two beds are exceedingly similar, the latter, in fact, 

 having been derived by erosion from exposed areas of the former. 



Splitting of shale formations seems a less common phenomenon. Two 

 good cases, however, come to mind. One was only recently described by 

 Morse and Foerste.®^ This is the black shale in central Kentucky com- 

 monly known in literature as the Ohio shale, or, more properly, as the 

 Chattanooga shale. Traced northwardly into Ohio, this bed of shale 

 s})lits into two parts, the upper being known as the Sunbury shale, the 

 lower as the Cleveland shale. These diverge more and more until in 

 northern Oliio both are subordinated in volume to the intercalated Berea 

 grit and the Bedford shale. The second case is that of the Woodford and 

 Caney shales in Oklahoma. Locally, these two black shale formations 

 succeed each other, and they are distinguished chiefly by the fact that the 

 lower (Woodford) contains a considerable amount of thin, platy chert 

 never seen in the upper. But this chert is sometimes scant or wanting in 

 the upper 100 feet or so of the Woodford, in which case the contact be- 

 tween the two formations is difficult to locate. At other localities in the 

 region of the Arbuckle uplift this contact diverges until it includes 300 to 



Journal Geology, vol. xvii, 1909, p. 164-177. 



