t 



PRINCIPLES OF STRx\TIGRAPHIC CORRELATIONS 521 



being chiefly on faimal and stratigraphic evidence. Still, in the matter 

 of constancy of lithologic characters and geographic extent, the Lowville 

 is perhaps the most notable of all Paleozoic limestone formations. 



Scarcely less excellent cases of persistence of lithologic character occur 

 among the shale and calcareous sandstone formations. Good examples 

 are the Utica black shale, distributed from Cincinnati to New York, the 

 greenish or bluish Eden shale horizon, which is unmistakably recognizable 

 in outcrops and in deep wells from Kentucky to central New York and in 

 the Appalachian shale formations from Pennsylvania to Tennessee, and 

 the Cincinnatian calcareous ''Bays^' sandstone, which maintains its pet- 

 rological characters and stratigraphic position in the middle and western 

 synclines of the Appalachian Valley from Pennsylvania to Tennessee. 

 The essential contemporaneity of geographically widely separated de- 

 posits in these and many other instances that might be mentioned of 

 lithologic constancy among Paleozoic formations is clearly established 

 by paleontologic and diastrophic evidence and by stratigraphic position. 

 Lithologic similarity, therefore, when checked by these other criteria, is 

 an important and usually reliable means of correlation. 



(2) Sandstones often of low value in correlation. — Relatively pure 

 quartz sandstone formations are not generally of value in determining 

 contemporaneity of deposition. Of the different kinds of sedimentary 

 rocks, sandstones, viewed as a class, are the least reliable for such pur- 

 poses. This is particularly true of sandstone deposits at the base of an 

 overlapping formation. Any sandstone immediately following a much 

 older formation, or separating two formations proved by fossil or other 

 evidence to be widely different in age, is to be regarded as probably vary- 

 ing in age from place to place according to the progress of a transgress- 

 ing sea. Notable examples are (1) the Lamotte sandstone and the Rea- 

 gan sandstone, respectively, at the base of the overlapping upper Cam- 

 brian in Missouri and Oklahoma; (2) the sandstone of the "Saint 

 Peter" group, which overlaps northwardly, so that its base is older in 

 Arkansas than ia Minnesota; (3) the sandstone of the "Oriskany" 

 group, which in crossing the State of New York from the east to the 

 west rises stratigraphically ; (4) the sandstone at the base of the over- 

 lapping Kinderhook series in northern Arkansas and southern Missouri, 

 and (5) the Trinity sandstone, which registers the slow advance of the 

 Cretaceous sea from Texas into the States north of it. 



For obvious reasons such overlapping sandstones are to be counted 

 with diastrophic criteria rather than the purely lithologic. As tending 

 the other way I would mention certain sandstone formations, like the 

 XXXV— Bull. Geol. Soc. Am., Vol. 22, 1910. 



