in changing such original minerals as the micaceous and 

 felspathio ingredients of crystalline rocks. From a com- 

 parison of formulae representing tourmaline and felspar, it 

 is evident that the act of tourmalinization has been accom- 

 panied by a loss of soda (which alone is capable of action 

 on tin.) The excess of boric acid( which is over and above 

 that required for tourmalinization) will combine with this 

 soda, forming metaborate and pyroborate of soda. 



"The former, acting on disseminated tin ore, might re- 

 sult in the production of sodium-metastannate and borax. 

 The soluble meta-stannate is capable of being leached out 

 of the magma, and, by a new reaction, tin oxide may be 

 precipitated and concentrated, sodium metaborate being 

 liberated." 



Again is to be remarked, in connection with this highly 

 scientific hypothesis of origin of tin ores, that at Winslow 

 are to be found in abundance all the necessary ingredients 

 to produce the chemical reactions described by MacAlister. 

 The presence of fluorine, boron, and tourmaline in profusion 

 in all the rocks of the Winslow series constitutes one of the 

 out-standing features of the mineralization there. And they 

 undoubtedly have exercised great, possibly predominant, in- 

 fluence in causing the precipitation of the cassiterite crystals 

 or tin ore of the veins. 



Among early visitors to the Winslow tin deposits was 

 the great Canadian mining geologist. T. Sterry Hunt, who, in 

 1873, in an address read at the Boston meeting of the Amer- 

 ican Institute of Mining Engineers of which he was then 

 President, referred to them in these words: 



"The White Mountain series in the Appalachians * * * * 

 abound in copper and have, moreover, yielded the only traces 

 of tin ore as yet known to us in Eastern North America. It 

 is with the gneisses and micaschists of this series that 

 cassiterite has been found in Massachusetts, New Hampshire 

 and Maine in concretionary aggregates with tourmaline, 

 beryl, micas, feldspars, fluorspar, et cetera, recalling the as- 

 sociations of the tin ores of Europe. At Winslow, in Maine, 

 the veins traverse a micaceous limestone which, I conceive, 

 belongs to this series * * * The veins, which are seldom more 

 than an inch or two in thickness are abundant through a 

 considerable breadth of the rock, and are interlaminated 

 with it, occupying places between the sedimentary layers, 

 which are distinctly marked by different shades of color. 

 Occasionally, however they cut across the stratification 

 for a little distance, showing that the disrupting action was 



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