BULLETIN OF THE GEOLOGICAL SOCIETY OF AMERICA 



Vol. 34. pp. 525-540 SEPTEMBER 30, 1923 



APPALACHIAN BAUXITE DEPOSITS ^ 



BY WILBUR A. NELSON 



{Read before the Society December 30, 1922) 



CONTENTS 



J 'age 



Introduction 525 



Physiography 526 



Geology 528 



Structure 529 



Bentonite and bauxite 530 



Analyses 532 



Laboratory experiments 536 



General conclusions 539 



Discussion 539 



Introduction 



In a paper given at the 1921 annual meeting of the Geological Society 

 of America;, entitled "A volcanic ash-bed in the Ordovician of Tennessee, 

 Kentucky, and Alabama," the following statement was made in regard 

 to a new theory of the formation of bauxite deposits : 



"Experiments made on bentonite show that when boiled with five times 

 normal solution of sulphuric acid for five hours the colloidal properties are 

 destroyed ; that about 85 per cent of the aluminum oxide goes into solution 

 as aluminum sulphate, along with the alkalies present, but that all the silica 

 except a trace remained undissolved. This fact offers a possible solution to 

 the origin of bauxite, as laboratory experiments show that such a solution of 

 aluminum sulphate is precipitated by a solution of tannic acid after standing 

 for a few days. Deposits of bentonite occurring in contact with pyritiferous 

 rocks would readily have part of their aluminum contents dissolved out by 

 the sulphuric acid in the ground-water, and such a solution of aluminum 

 sulphate, it seems, would be precipitated by natural reducing agents, such as 

 tannic acid or acid peat-forming bacteria, and thus form certain of our present 

 bauxite deposits." 



Following these experiments, it was decided to visit the Chattanooga 

 bauxite deposits and make a detailed study of the geology of the Mission- 



1 Manuscript received by the Secretary of the Society January 29, 1923. 



(525) 



