Character of Sediments. . £23 
to each other and to present sealevel, but not to sealevel in past 
time. The lowest line, P, the present flood plain of the Ten- 
nessee river, is 650 feet above sealevel ; the second, 7, the Ter- 
tiary peneplain, is 250 feet above the present river; the third, 
K, the Cretaceous peneplain, is about 1,100 feet above the Ter- 
tiary ; and, last, the original land surface is about 5,000 or 6,0Q0 
feet above the Cretaceous baselevel. 
Part ITI—Sepimentary Recorp. 
The variation in character of sediments deposited on the 
southern border of the Appalachian province during Cretaceous 
and later time has been briefly referred to, and also the correla- 
tion between kind of sediment and attitude of land. The con- 
clusions reached by other lines of evidence are so fully borne 
out by a consideration of the sediments that the subject merits 
a somewhat fuller treatment. The character of sedimentary 
rocks is usually regarded as indicative of the depth of water in 
which they were formed, and while this is in a measure true, a. 
more important element is probably the character and attitude 
of the adjacent land from which the sediments were derived. 
High land is subjected to active degradation, especially if it 
has been recently elevated and is covered by a heavy mantle of 
residual material. Its streams have rapid fall and are supplied 
with an abundant load of coarse mechanical sediment which 
they carry in great volume to the sea. Under such conditions of 
rapid erosion the deposits formed are gravels, sands and clays, 
generally highly colored from the complete oxidation of the re- 
sidual mantle before transportation. Solution is at the same time 
going on, butethe volume of material removed by that means is 
small in comparison with the mechanical sediment, and the pro- 
portion of calcareous matter is correspondingly small in the de- 
posits formed. As the cycleadvances the gradients of the streams 
decrease, and with it their carrying capacity. Hence the pro- 
portion of matter in solution is increased by the diminution in 
the absolute amount of mechanical sediment and the deposits 
become correspondingly more calcareous. In the final stages of 
baseleveling, chemical agents are more active than mechanical ; 
the sluggish streams are able to transport only the finest silt in 
suspension and the resulting deposit is a more or less pure 
limestone. The character of the sediments derived from the 
