512 PHYSICAL GEOGRAPHY. 



sediments, we look in vain over the broad expanse of waters for any 

 landmark to indicate the boundaries of New Hampshire or the neigh- 

 boring states. Towards the close of this epoch, and probably after the 

 formation of large islands to the north in Canada, and to the west in 

 New York (Adirondack region), oceanic currents began to accumulate 

 sediments in the shallower places. After a while these masses attained 

 large dimensions; and the operation of igneous forces beneath brought 

 to the surface an archipelago of islands, perhaps thirty in number. 

 These constituted the first areas of dry land in New Hampshire. The 

 position and shapes of these islands, as the rock composing them now 

 crops out, are shown in the first of our series of illustrations. 



These islands were probably composed of clay and sand. The clay 

 may have come from the decomposition of still earlier feldspathic rocks, 

 possibly the original crust of the earth. The sand may have been 

 washed from some of the primeval piles of superfluous silica, which 

 found no congenial element with which to unite in the world-making 

 process. As these areas are now examined, they seem to be composed 

 chiefly of porphyritic granite or gneiss, which, to ordinary eyes, appear 

 to be very unlike clay and sand. Is it possible that the sediments have 

 been altered into these crystalline aggregates? 



The answer to this question involves propositions the most difficult of 

 any in our science to be lucidly explained. It is only sufficient now to 

 state our theory. These primeval deposits of sand and clay, by the 

 action of steam, heat, and chemical agents, have been changed into 

 gneiss and granite. The large crystals of feldspar and the scales of 

 mica are the products of the alteration of clay. The sediments are sup- 

 posed to have been rendered soft and plastic through heat and steam ; 

 and chemical affinities have collected together, from a heterogeneous 

 mass, all the elements required to form the two crystalline minerals. 

 After their crystallization, the residuum, consisting of amorphous silica, 

 sought the crevices between the newly formed minerals, became closely 

 packed because of a considerable pressure crowding the mass, and have 

 had no opportunity of assuming the geometrical shapes forming when 

 the quartz is situated in favorable situations. This change is known as 

 metamorphism. 



The resultant rock attracts attention by its spotted appearance. One 



