76 TJic American Geologist. Anijust, i89i 
heat is clearh' one of the most important. Again, in spite of the 
recent glaeiatiou, evidences of kaolinization are not wanting in the 
North ; Ijut the resulting claj", the true sedentar}' soil of the 
North, is never red, indicating very plainl}' that, while a warm 
climate is not stricth' essential to the formation of residual clays, 
it is a necessar}- condition of the development of the red color. 
Prof. J. D. Dana emphasizes this point in a review * of Mr. Rus- 
sell's work, from which a few sentences ma}' be quoted : 
The contrast in colors between the northern and southern states is 
spoken of (by Russell) as " contrast between a glaciated country and a 
region in which atmospheric decay has progressed uninterruptedly for 
ages." Mr. Russell, knowing less of New England than of other parts 
of the country, does not appreciate as strongly as professor Crosby, 
whom he criticises, the full character of this difference. There is wide 
decomposition at tiie North, and its rapid progress in the case of syen- 
ites, mica schists, gneisses, granites, and hornblende schists during the 
past forty years, is very strikingly exhibited alongside of many railroad 
cuts. The fact to be accounted for is that these decompositions over 
New England, whether in the trap of trap dikes or in metamorphic 
rocks, produces almost nev&r red earth ; while at the South, red earth 
predominates. The glacial movements and orographic changes have 
nothing to do with this. The fact is simply that in New England the 
result of the iron oxidation attending the decay is limonite, the hydrous, 
yellow-brown iron oxide, and not anhydrous Fe^O^. The writer has often 
tried to discover a reason for the different result at the South ; he does 
not find one in Mr. Russell's excellent paper. 
In what manner, if an}', the milder climate of the South pro- 
motes the development of the red color, except directly by favoring 
the dehydration of the iron oxide, I have not attempted to explain; 
but when we consider that, aside from the glaciation of the North, 
there is virtual!}' or primaril}' but this one physical contrast be- 
tween the North and South, it seems impossible to doubt the 
existence, directh^ or indirect!}', of a casual connection between 
the temperature and the color of the soil. The fact that Mr. Rus- 
sell questions this conclusion caused me, however, less surprise 
than his attempt to fortify that negative position by denying that 
the red color of southern clays is essentially a superficial feat- 
ure. I was amazed at his statements in this regard, and asked 
myself again and again if my recollection of what I had seen in 
the gold mines of North Carolina and elsewhere could possibly be 
so far astray. Being unwilling to controvert the views of so com- 
petent an observer without a fresh examination of the facts, I have 
waited for an opportunity to go over the ground again. Fortunately, 
» American Journal of Science, Volume XXXIX., 1890, pp. 317-3U>. 
