Effect of Land Warping on Drainage. 119 
the drainage of the Appalachian valley assumed practically the 
form which it has today. 
As indicated in the above discussion of drainage adjustment, 
the present writers have reached the conclusion that an ex- 
tremely important factor in the process is the slow and gentle 
warping of the surface which has accompanied every epeirogenic 
movement of which there is any record. We believe this factor 
is only less important than the great structural features of a 
region, and in some eases, of which the Tennessee is a notable 
example, the structure of the region has played a secondary 
part in determining the drainage courses. This gentle warping 
of the surface has hitherto been recognized only in a general 
way and few attempts have been made to locate axes; conse- 
quently the manner in which it influences drainage has not yet 
been discussed. The writers have in preparation a paper in 
which an attempt will be made to formulate the laws of this 
action and to show much more fully than the limits of the 
present paper will permit to what extent it has determined the 
courses of the Appalachian streams. 
3.—PRESENT CYCLE. 
Northward diversion of the Tennessee River—The Lafayette de- 
pression, with its accompanying deposition of coarse sediments 
about the border of the province, occupied the closing epoch of 
the Tertiary cycle. The next, which may properly be termed 
the Present cycle, was inaugurated, like the two preceding, by 
uplift, and the uplift was accompanied by warping of the surface. 
The southern portion of the province was tilted northward, prob- 
ably somewhat beyond the Memphis-Charleston axis. The 
rivers whose lower courses had been rendered sluggish or even 
submerged by the preceding depression were stimulated to 
renewed activity and began a rapid trenching of the lately de- 
posited Lafayette formation. The land area was extended con- 
siderably beyond its present limits, and the rivers throughout 
their lower courses cut deep gorges, forming notches in the 
present submerged continental shelf. The uplift along the 
southern border of the province was so rapid that only the larger 
streams or those favorably located upon soft rocks were able to 
keep their channels down near baselevel. The Alabama river, 
although only the shrunken representative of the once powerful 
Appalachian river, had its lower course located on sqft Tertiary 
17—Nar. Grog. Maa., von, VI, 1894, 
