Page:The Journal of geology (IA journalofgeology11893univ).pdf/298

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 oxidation of the metalliferous solution and the precipitation of oxide or carbonate of manganese,^[1] 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,^[2] 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,^[4] as well as the waters in some of the mines at Freyberg,^[5] also form manganiferous 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 incrustation of oxide of manganese is deposited by rivers and creeks on the rocks and pebbles in their courses are of common occurrence.