78 The Americaji Geologist. August, jsoi 
schist, measuring, in this instance, less than 12 feet, and the red 
clay less than 3 feet. More recently, I have collected a similar 
series in the vicinity of Rock creek, in the District of Columbia. 
In connection with his criticism of m}' views, Mr. Russell refers 
to a quotation, on an earlier page of hisessa}-, from an account bj' 
Prof. E. A. Smith of the residual cla3S of Alabama^ Professor 
Smith's description, so far as it is pertinent to the present dis- 
cussion, is as follows : 
The soil of the red lands is derived from the decomposed hornblendic 
gneisses and slates, which in many places, where exposed in washes or 
gullies, are seen to be mere stratified clays, containing fragments, more 
or less angular, of the quartz veins or seams, which are nearly always 
interbedded with the other rocks of this region. The top stratum of 
this soil, from two to three inches in depth, has often a dark chocolate- 
brown color, but below it becomes a bright red, and at varying depths, 
from ten to fifteen feet, becomes a yellowish, hard clay. ]Vhere the 
freshly decomposed rocks are seen the color is yellowish rather than red, 
the latter color (red) being darker and more inte7ise, apparently, the 
fiwther removed Vie soil is from its original position and the more it is 
affected by the decay of the vegetable matter. 
The italics are my own ; but how this description lends any sup- 
port to Mr. Russell's criticism is certainly not very clear ; on the 
coutrar}', it coiToborates my statements that the red color is limited 
to the vicinity of the surface, and that the deeper and newer clay 
in every normal section is yellow. Professor Smith's description 
( which would apply equall}- well to large areas in Georgia ) indi- 
cates, what might naturally be expected from the lower latitude, a 
greater average thickness of the red cla}' than I have observed in 
North Carolina and Virginia. 
Whatever the cause of the superficial dehydration of the ferric 
oxide, changing the color from j'ellow to red, it is unquestionably 
a slow process ; and since the red portion of the soil is clearly the 
oldest part, residual, unlike sedimentar}-, deposits growing from 
the top downward, we ma}' find here an eas}' and suflScient expla- 
nation of the point in Mr. Russell's criticism to the eflfect that " over 
considerable areas in the South the surface clays are various shades 
of yellow, which would not be expected if the red color of adjacent 
fields is due to temperature " ( page 42 ). We have only to sup- 
pose that erosion, which acts upon all areas in some degree, is 
here sufficiently rapid to prevent the development of the red color, 
removing the clay before it has time to change its hue. Mr. Rus- 
sel has pointed out xevy clearly that the simple existence of the 
^Geological Survey of Alabama, Report for 1881, and 1882, p. 184. 
