338 E. O. ULRICH REVISION OF THE PALEOZOIC SYSTEMS 



of a given fauna, may correctly anticipate the discovery of such buried 

 channels by the driller. Such an instance is given on page 423, where 

 thick Devonian and other formations, wholly absent in the exposed 

 stratigraphic succession on the west flank of Ozarkia, are mentioned as 

 being found in a deep well at Forest City, Missouri. It may be argued 

 that the failure of these concealed formations to outcrop in Missouri is 

 due either to removal of the deposits by erosion or that their deposition 

 was prevented by current scour along a shore. For various reasons I can 

 not admit either suggestion. As I see the case, it means only that the 

 channel or basin to the northwest of Ozarkia was narrower at such times 

 and the lands larger. As for the concealed formations themselves, they 

 mean nothing more or less than overlapping sediments whose final stage 

 fell short of stages attained in subsequent submergences. 



Initial submergences often larger than succeeding invasions of same 

 stage or period. — That the advance of the sea into the continental de- 

 pressions, especially of the median areas, was probably never continuous 

 through the whole or even the greater part of a geologic period is con- 

 vincingly indicated by the fact that the advance in the early part of a 

 stage often exceeded later invasions of the same stage. It is a fact, too, 

 that the geographic pattern formed by the distribution of land and water 

 areas in these later ages differed from that of the early phases generally 

 not only in that the areas submerged were smaller, but more in that the 

 seas were shifted partly or wholly into other basins. Body deformations, 

 resulting in warping and differential oscillation of the lithosphere, the 

 latter phenomenon to be later described under the designation "tilting,'^ 

 are primarily the cause of these differences in geographic aspect. 



The idea is illustrated by the varying stages of the Ozarkian seas. 

 Thus the early Saratogan, represented in New York by the Potsdam 

 sandstone, elsewhere by either sandstone or dolomite, seems to have 

 spread as widely in the United States as any sea of this period. In New 

 York it is found on both the east and west sides of the Adirondacks, and 

 corresponding beds are recognized in the Appalachian Valley, in Mis- 

 souri, and in the upper Mississippi Valley. Now the passage from the 

 early (Potsdam) stage of the Saratogan to the lime-depositing middle 

 phase involved a geographic change. This is shown in New York by the 

 restriction of the sea to the east and south sides of the Adirondack 

 mass. There were marked changes, also, in the Appalachian Valley, 

 where the waters retreated to the south and west; also in Missouri and 

 in the upper Mississippi Valley, where considerable sea shifting occurred 

 at this time. The new (Gasconade) distribution continued through a 



