Williams — Age of Manganese beds of Arkansas. 325 



2. The increase in self-induction produces greater damping 

 and a shortening of the wave length of 1*5 to 2 per cent. 



3. The permeability p. of annealed iron wires under this rate 

 of alternation is about 385. 



4. For oscillations of the same period, the wave length along 

 parallel copper wires varies directly with the diameter of the 

 wires. Range of wires used O03915 crn to 0-1201 cm . The max- 

 imum decrease observed is 5 per cent. 



Jefferson Physical Laboratory, July 24, 1894. 



Art. XLYI. — On the Age of the Manganese beds of the Bates- 

 ville Region of Arkansas ; by Henry S. Williams. 



The following quotations from his admirable monograph on 

 Manganese* represent the chief points of Dr. Penrose's inter- 

 pretation of the origin and age of the Batesville manganese 

 ores. 



The Batesville ores were precipitated, from surface waters 

 draining southward from the Arcbrean region of Missouri. The 

 area of precipitation was originally a region of comparatively 

 quiet water bounded on either side by rapidly flowing cur- 

 rents ; this condition allowed the excessive accumulation of marine 

 sediments and caused a greater thickness of the St. Clair lime- 

 stone than to the east or west ; the detritus from the land was 

 carried down and mixed with the calcareous materials, the grad- 

 ual accumulation of these mixed sediments caused shoals and 

 then created lagoons and swamps into which the surface waters 

 from the land emptied, and by a process of oxidation and evapo- 

 ration deposited the metaliferous matter that they carried in solu- 

 tion. (1. c, p. 595.) 



The process of formation of the manganese deposits as they 

 now exist is supposed by him to have been by the decay, in 

 situ, of the St. Clair limestone. 



The deposits of manganese ore in the Batesville region that 

 can be profitably worked are not found in place in the limestone. 

 [The Cason property excepted] ... it is only when the limestone 

 or "gray rock," as it is commonly called, has been decayed, the 

 carbonate of lime carried off in solution, and the masses of ore 

 with the residual clay thus set free and concentrated, that profit- 

 able mining can be done. This decay has taken place on an im- 

 mense scale, and all the deposits that are being worked, and all 

 that have been worked in the past, with the exception of the 

 Cason mine, represent such products of decay. (1. c, p. 174.) 



*Ann. Rept. of Geol. Surv. of Arkansas for 1890, vol. i. Manganese: its 

 uses, ores and deposits, by R. A. P. Penrose, Jr., Ph.D. 



