40 The American Geologist. juiy. inoi. 
bodies are free from inckuled residual material. The concen- 
tration or accumulation of ore deposits from weathering- /// situ 
usually shows more or less residual material variously admixed, 
which fonns the most convincing evidence in the case of de- 
posits derived from rock weathering. This point is abundantly 
illustrated in the manganese and some of the iron deposits in 
the same region. (3) The relation of the deposits to the pres- 
ent topography of the region and their altitude above sea 
level. Upon Dr. Spencer's theory the ore-bodies if they repre- 
sent accumulation from weathering of the Knox limestone 
should only occur at definite and uniform positions in that for- 
mation. On the contrary the deposits do not conform to these 
conditions, but are found in all parts of the Knox dolomyte, 
giving as Hayes* has shown, a stratigraphic range of at least 
4,000 feet. (4) While the bauxite deposits in question 
are somewhat closely associated with those of iron and mangan- 
ese, more particularly the iron, it by no means follows that the 
conditions suggest a "common genesis." In fact, recent work 
in this area conclusively demonstrates that the three types of ore" 
bodies are not of a common genesis. The manganese deposits of 
the Cartersville district represent undoubted residual accumu- 
lations concentrated by physical and chemical processes inci- 
dental to weathering. The ore deposits of iron and manganese 
are more intimately associated than any two metalliferous de- 
posits known in the area and yet with several exceptions they 
have had a different origin. 
The above facts constitute some of the essential featiu-es of 
the bauxite deposits which must be accounted for in any satis- 
factoiT explanation. 
After a detailed study of the structural geology of the re- 
gion and of the ore-bodies Dr. C. W. Hayest suggests a the- 
ory for the origin of the Georgia deposits which is entirely dif- 
ferent from the one formulated by Dr. Spencer. Hayes' the- 
orv is briefly stated by him as follows ':$ 
"The deposits are there [Georgia- Alabama region] found 
embedded in residual clay derived from the weathering of lime- 
stone. The limestone overlies a great mass of shales, and the 
*Op. cited. 
tBauxite, Sixteenth Annual Report. U. S. Geol. Survey, 1S95, part iii, pp. 
587-591. This contains a very full and detailed statement of Dr. Hayes' tlieorv. 
JTaken from the proof copir of Dr. Haj-«s' verj- valuable paper on "The 
Arkansas Bauxite Deposits," not yet issued from the press, but the author 
Dr. Hayhs very kindly placed at my disposal a proof copy of the report. 
