Deposition of Lafayette Gravels. 115 
ward, increasing its slope.. There was also some warping on the 
lateral axis, so that the depression on A B was less in the Appa- 
lachian valley than on either side. As the first result of this 
depression, the sea, which had retreated beyond the present Gulf 
coast during the Tertiary, advanced past the inner limits of Ter- 
tiary and Cretaceous sediments, while the Mississippi embayment 
became a broad, shallow gulf and a portion of the Sequatchie 
valley a narrow tidal estuary. During this depression the La- 
fayette formation was deposited. The previously baseleveled 
streams, by the warping of the land, were accelerated in the in- 
terior and brought down vast quantities of detrital material 
which had accumulated during a long period of subaerial rock 
decay. This was spread out mantle-wise over the submerged 
border of the province and along the lower courses of the streams 
where their currents were checked. These gravels are found on 
the remnants of the Tertiary peneplain about Chattanooga, 250 
feet above the present river; they are also found on the Tertiary 
peneplain in Sequatchie valley, 150 feet above the river, but so 
far as known they are entirely absent from the divide between 
the Tennessee and Coosa rivers. These gravels have the same 
character on both sides of Walden plateau, being composed of 
quartzite and vein quartz, of which the latter at least must have 
been brought from far to the eastward ; therefore it appears cer- 
tain that the Appalachian drainage was diverted from the present 
Tennessee-Coosa divide westward to its present course through 
the Walden gorge very early in the period of Lafayette depres- 
sion. Following this period of depression came one of uplift, 
when the streams of the province were stimulated to renewed 
activity and began cutting the present river channels. That the 
Appalachian drainage was diverted to its present course before 
this uplift is quite certain, for no channels are cut in the Tertiary 
peneplain across the Coosa-Tennessee divide. 
Manner in which the Diversion was accomplished.—Having fixed 
its date in geologic time with a fair degree of certainty, the pro- 
cess by which the diversion was effected may now be described 
in detail. The conditions which prevailed in the region between 
Chattanooga and Sequatchie valley during the Tertiary cycle 
have been already described. With the uplift at the beginning 
of that cycle the main southward flowing streams rapidly sank 
their channels on the soft limestone, while their tributaries began 
an active contest for the intervening territory. The axial uplift 
