454 E. O. ULRICH REVISION OF THE PALEOZOIC SYSTEMS 



These have not only established that such movements actually took place, 

 but their evidence has proved of the highest value in unravelling per- 

 plexing problems of correlation. Without such evidence the attempt to 

 prove that the Carter division of the Stones Eiver group does not out- 

 crop on the east side of the Nashville dome, and that beds on that side 

 which seemed to occupy the same stratigraphic position and were in fact 

 correlated with the Carter by Safford are really Lowville, hence younger, 

 might well have failed to convince. But the task lost most of its diffi- 

 culties when a thin wedge of Lowville was found resting unconformably 

 on the Carter near Nashville; and the correlation became easily con- 

 vincing when typical magnesian Carter limestone was found at High- 

 bridge, Kentucky, beneath a full Lowville section. 



For similar reasons, although strongly suggested by differences in 

 faunal contents, it would have been difficult to prove the alternating 

 transgressions of Arctic, Pacific, and Gulf of Mexico waters, described 

 on pages 367 to 371, if the thin wedges of northern formations had not 

 been found in Kentucky and Tennessee and if it had remained unknown 

 that the Kimmswick limestone passes under southward extensions of 

 lower members of the Galena group in northeastern Missouri. Or, 

 taking another case, to prove that the Maquoketa shale, which closely 

 simulates the Utica in appearance and fauna, is really of middle Eich- 

 mond age, if we did not know from unequivocal evidence in eastern 

 Missouri and west central Tennessee that it overlies two lower Richmond 

 formations — the Fernvale, and beneath this the Arnheim. Evidence of 

 this nature is simply incontrovertible. In short, no other evidence is so 

 trustworthy in disproving supposed synchrony of deposits which have 

 been correlated chiefly or solely on fossil evidence, or because of apparent 

 likeness in stratigraphic position, as that of stratigraphic overlaps. Nor 

 is any so valuable in narrowing the limit of possible error in correlating 

 disconnected lithologic units that happen to be included between two 

 more widely transgressing formations. 



PECULIARITIES OF INITIAL DEPOSITS AT BASE OP OVERLAPPING FORMA- 

 TIONS 



Ordinarily we expect to find a layer consisting wholly or in part of ill- 

 assorted clastic material at and rising with the bottom of an overlapping 

 formation. Sometimes it is a sandstone the grains of which are likely 

 to be rounded; or it is a conglomerate the pebbles of which may have 

 been derived from the immediately underlying rock or from many near 

 to distant sources. Again the basal layer is a mudrock, in one case com- 

 posed mainly of clay, in another calcareous enough to be called a lime- 



