508 PHYSICAL GEOGRAPHY. 



Of these great eras, New Hampshire furnishes quite fully the forma- 

 tions accumulated during the first, and somewhat of the second. After 

 that, there are hints as to her condition derived from general considera- 

 tions, which will be mentioned in the proper place. The Eozoic era is 

 divided into the Laurentian, Atlantic, Labrador, and Huronian periods 

 in New Hampshire. 



The following considerations lead us to believe that life existed in 

 these periods. 



I. The presence of ores of iron is an evidence of the existence of 

 vegetation. Ores of iron are conceived to have been formed similarly 

 in all ages. At the present day they accumulate in swamps and low 

 grounds in the form of bog ore, or the hydrated peroxide (ferric). To 

 effect this deposition the presence of organic matter is requisite. The 

 iron is present in the soil in small proportion, as the insoluble ferric 

 oxide. Vegetation, when soaked in water, imparts to it the capacity of 

 dissolving this ferric oxide. A portion of the oxygen is given off, and 

 the compound becomes the ferrous oxide, and in this condition is readily 

 soluble. But this is not a stable compound in the presence of the atmos- 

 phere. There are new combinations, and the soluble ferrous, or protoxide, 

 is changed to the insoluble hydrated peroxide, and is precipitated, falling 

 to the bottom. This process being continued indefinitely, there accumu- 

 lates a large thickness of the bog ore, oftentimes sufficient to furnish 

 material for the smelter. 



It is supposed that most of the ores of iron in every age have been 

 formed in this way. As the modern bog is now essential to their pro- 

 duction, so must there have been vegetation in the most ancient periods 

 to eliminate the iron. 



Furthermore, the Laurentian vegetation must have been extremely 

 abundant, on account of the enormous deposits of iron ores seen in the 

 Adirondacks, Ontario, Missouri, etc. There are beds hundreds of feet in 

 thickness. This proof is afforded by certain beds in New Hampshire, as 

 in Lisbon (Franconia) and Landaff. The beds in Bartlett and Gilford 

 are in granite, and may possibly have come from igneous action, and if 

 so are likely to be limited in quantity. 



Chemical changes have taken place in the original bog ore in order to 

 produce the magnetic ore of Lisbon. This is two-fold. First, the water 



