PHYSICAL HISTORY OF NEW HAMPSHIRE. 51/ 



Berlin and Lebanon, chiefly in the Connecticut valley and in Carroll 

 county, of sandy grits, which we know in the altered state as the Bethle- 

 hem grotip. 2. It is likely that these strata were elevated and metamor- 

 phosed at the close of this era. 3. The very extensive deposits of the 

 Lake gneiss formation were next laid down. The largest amount of them 

 underlie the hydrographic basin of Winnipiseogee lake, and follow the 

 porphyritic band south-westerly towards Peterborough. The same group 

 extends from southern Cheshire county, through Sullivan and Grafton 

 counties, to Milan, and also from Mason to Deerfield, through Man- 

 chester. 4. Nearly all the rest of the Atlantic area,- or the Montalban 

 group, was next deposited. The rocks are of two or three kinds. There 

 is a gneiss, largely deficient in feldspar, containing crystals of andalusite 

 in abundance. This characterizes the principal White Mountain sum- 

 mits. A second variety is excessively ferruginous upon decomposition. 

 A third is the well known "granite" of Concord, Plymouth, Farmington, 

 Milford, Fitzwilliam, Troy, Marlborough, etc. It is really a stratified 

 rock, whose divisional planes can be detected only with great difficulty. 

 There must have been variations in the conditions of deposit to insure 

 the accumulation of sediments that should alter into schists so diverse 

 from each other as these. 5. Next came the ejection of the granitic 

 mass, giving rise to the Franconia breccia. This igneous rock is com- 

 pletely filled with masses of all the formations that have been described 

 thus far, but carries none of those that succeed. Hence it seems to 

 have been connected with the great series of disturbances closing the 

 long period of quiet Atkntic deposition. This rock covers a few square 

 miles in Franconia, and may be repeated in Granby, Vt., and possibly at 

 one or two places along the Connecticut valley. The paste of the breccia 

 is mostly feldspathic in its mineral constitution. 6. Next came probably 

 the greatest period of disturbance and elevation known in the whole his- 

 tory of New Hampshire. The White and Green mountains came into 

 being, and, most likely, the whole system of Atlantic mountains, from Can- 

 ada to Alabama. They may not have assumed their present elevation at 

 this time, but became a marked feature in the primeval landscape, and 

 prominent objects for the action of the atmospheric elements, breaking 

 down and washing away all jutting out points. In connection with the 

 elevation, the sedimentary strata became converted into crystalline schists. 



