GHOLOGICG, VERSOS EITHOLOGILE 239 
of Tertiary deposits in the Coastal Plain region, and even in 
establishing the boundary between Cretaceous and Eocene sys- 
tems, although that line may represent a stratigraphic break. 
Thus in the Uvalde quadrangle of Texas Mr. T. Wayland 
Vaughan describes the uppermost Cretaceous and the adjacent 
Eocene formations as presenting such complex and rapidly 
changing lithologic characters, and as so similar in these varia- 
tions that the stratigraphic line of much significance between 
them is not determinable except on fossil evidence. From litho- 
logic character one would necessarily conclude that conditions 
of sedimentation alternated irregularly through the period rep- 
resented by the section in question and no one line of change 
would be suggested as of special importance, or at least the one 
which is of greatest significance would not be indicated. There 
is, however, a sharp line present, indicated by the fossils of two 
beds in close proximity, one carrying a Cretaceous fauna, the 
other Eocene forms, and no single species of either the exten- 
sive Cretaceous fauna below, or of the Eocene above, has been 
found to cross this line. The use of this information in dis- 
criminating cartographic units is thus essential to a representa- 
tion, which is entirely practicable, of important geological facts 
concerning this quadrangle and the Gulf province to which it 
belongs.* 
Another example of the insufficiency of lithologic characters 
alone as means of discriminating the desirable cartographic units 
of a province is afforded by the southern Appalachian region. 
At the time when the areal work of the United States Geologi- 
cal Survey there was in charge of Mr. Willis, he described the 
conditions as regards the Paleozoic section as follows: 
Thus the Paleozoic sediments are a great complex of lenses of every 
grade of lithologic character, from pure limestone to conglomerate, and litho- 
logic distinctions cease to be of value except when used as guides in small 
districts or when variations are traced out by continuous detailed study.” 
Mr. Willis further explains (in the same place) that as a 
1“ Uvalde folio,” Geologic Atlas of U. S., No. 64. 
2 Tenth Ann. Rept. U. S. Geol. Surv., p. 121. 
