282 THE JOURNAL OF GEOLOGY. 



deposit was due to a local precipitation brought on by an excess 

 of manganese in spring waters in the locality in question, and 

 that the cause of its accumulation was the accidental formation 

 of a suitable basin in the tufa. This basin may either have been 

 closed or may have had an outlet into the lake. When the 

 spring waters reached the surface they were probably retained, 

 at least temporarily, in the basin, long enough to allow the oxida- 

 tion of the metalliferous solution and the precipitation of oxide 

 or carbonate of manganese,^ thus causing a local accumulation of 

 ore ; whereas, if the spring water had flowed directly into the 

 lake, its contents of manganese would have been scattered over 

 a vast area, and would not have accumulated anywhere in 

 deposits of noticeable size. The rock fragments in the ore and 

 tufa represent detritus from the mountain side carried down 

 during the deposition of the beds. 



The deposition of manganese by spring waters elsewhere 

 than in the case in question, though in limited quantities, is not 

 an unusual occurrence. The Hot Springs of Arkansas deposit a 

 calcareous sinter often heavily impregnated by manganese. A 

 hot spring near the Cape of Good Hope,^ with a temperature of 

 110° Fahrenheit, deposits oxide of manganese in its discharge 

 channel. A mineral spring in the house of the Russian Crown, 

 at Carlsbad, 3 with a temperature of 68° Fahrenheit, also forms 

 manganiferous deposits. The springs at Luxeuil,'^ as well as 

 the waters in some of the mines at Freyberg,^ also form mangan- 

 iferous sediments. These deposits, however, are all very small 

 and are simply mentioned to show the frequent occurrence of 

 manganese deposited by springs. Cases where a black incrusta- 

 tion of oxide of manganese is deposited by rivers and creeks on 

 the rocks and pebbles in their courses are of common occur- 

 rence. R. A. F. Penrose, Jr. 



^ If the carbonate was precipitated, it was later converted by oxidation into its 

 present oxide form. 



2 Townsend, r Institut., 1844, No. 529. (Bischof.) 



3 Kersten's u. v. Dechen's Archiv. f. Mineral., etc., Vol. XIX., p. 754. (Bischof.) 

 "t Braconnot, Ann. de Chim. et de Phys., Vol. 18, p. 221. (Bischof.) 



5 Kersten's u. v. Dechen's Archiv. f. Mineral., etc.. Vol. XIX., p. 754. (Bischof.) 



