PHYSICAL HISTORY OF NEW HAMPSHIRE. 509 



has been expelled, perhaps by the action of heat. This would give rise 

 to hematite and specular iron, which differ from the original compound 

 only by the absence of water. Second, a further change, probably the 

 continued application of heat, expels a part of the oxygen, producing the 

 magnetic oxide, — a compound intermediate between the ferrous and ferric 

 oxides in respect to the amount of oxygen present. 



The preparation of the quartz of Lyndeborough for the manufacture 

 of glass illustrates the nature of the chemical changes which I have just 

 mentioned. The quartz as taken from the ledge is not perfectly pure, 

 since it contains a small per cent, of ferric oxide, perhaps combined with 

 water. This colors green the vessels manufactured from it, and therefore 

 it is best to eliminate the iron as completely as possible, so as to secure a 

 better quality of glass. The rock is put into a kiln and burnt, just as if 

 it were limestone being converted into lime. The rock becomes friable, 

 so that it can be readily crushed and pulverized, and the iron is converted 

 into the magnetic oxide. After pulverization, the quartz-flour is made to 

 fall in a stream over magnets set like bristles on the surface of cylinders. 

 The magnets instantly attract the iron sand, which is thus perfectly 

 removed from the quartz by several repetitions of the process of falling 

 over the revolving cylinder. Had not the fire removed the water and a 

 portion of the oxygen from the iron ore, the magnets could not purify 

 the quartz. The change is precisely like that which has taken place in 

 the magnetization of the Laurentian ore-beds, and hence it is reasonable 

 to suppose that nature has done the same work upon a large scale which 

 may be often witnessed at the Lyndeborough glass-works. 



2. The presence of graphite, plumbago or black-lead in the Eozoic 

 rocks is evidence of the former existence of vegetation. We do not yet 

 know how to account for the existence of graphite in the earth, except 

 through plants. Great changes have been effected in its mass, so as to 

 have entirely altered its nature. Instead of being combustible, it is one 

 of the most refractory substances known, and is largely used for the 

 manufacture of crucibles in which metals are fused. No one has yet 

 detected any traces of vegetable structure in graphite, so that we have 

 no evidence from morphology of the nature of the earliest plants. From 

 general considerations, we may believe them to have been algse, fungi, or 

 lichens, perhaps, of giant forms and of particular shapes not represented 



