MINERALOGY. 4/ 



where it has been deposited by sluggish streams. On Black mountain 

 in Haverhill there is a deposit of the compact botryoidal limonite. Bar- 

 rington, Gilmanton, Kingston, Mason, Lyndeborough, New Boston, Ches- 

 terfield, Nottingham, West River mountain. Orange, Pembroke, Salisbury, 

 Jaffrey, Moultonborough, Orford, Surry, and Plainfield are other towns 

 where deposits of the hydrous iron oxide are found. As may be inferred, 

 it is generally distributed all over the state, either as the compact, dark 

 mineral limonite, or forming ochrey beds of a foot or more in thickness, 

 and again, as a mere ferruginous deposit in the gravel, where it cements 

 the pebbles together. 



The mode of origin of limonite has been treated of by many writers. 

 The beds in this section of the country were shown by Percival * to have 

 resulted from the transportation and redeposition of the iron from decay- 

 ing pyritiferous rocks. Other writers have followed, showing the same 

 to be true of the other deposits that occur along the Atlantic coast. The 

 exact source of the iron can generally be ascertained by studying the 

 rocks of the region. The method of transportation has also received 

 much attention ; for, as the sesquioxide of iron is insoluble, if it were 

 transported in solution it must have been in some other condition. 

 There are many chalybeate springs in our state, several of which are 

 found near by the deposits of bog iron, and which show that here as 

 elsewhere the iron has in part been transported in the state of carbonate. 

 Sometimes by oxidation pyrites is converted into a sulphate of iron, and 

 thus transported, and, again, it is transported as a salt of an organic acid, 

 as suggested by Berzelius, and verified for our ores by Jackson,! who 

 analyzed these ores, and found varying amounts of organic acids in them. 

 Hunt, in the ochre of Pointe du Lac in Canada, found fifteen per cent, of 

 humic acid ; and Jackson's analyses show varying amounts from none to 

 eighteen per cent, of vegetable matter, which he refers to organic acids ; 

 but what proportion of this resulted from the vegetation of the swamps 

 in which the ores were deposited is not with certainty determined. Iron 

 transported in any of these ways is liable to be deposited as the hydrous 

 sesquioxide, as soon as it is subjected to oxidation, though a portion of it 

 may remain as carbonate; and more or less of the carbonate of iron 



* Rep. Ceo!. Conn., p. 132. 



t Geology of Netv Hampshire, Dr. C. T. Jackson, 1844 



