GEOLOGY OP MOUNT DESERT. 47 



arrangement of stratified or water-deposited rocks, indi- 

 cates that its materials were not brought here in fine 

 particles and in succession, and laid down in beds one after ^J 

 another ; but that the whole mass took its place essentially 

 at once, and that its structure was gained by a single 

 process, in operation practically at one time in all its parts. 

 Slow crystallization by cooling from fusion is the most 

 plausible explanation of such a result ; and this is borne 

 out by an examination of the structure of modern lavas, 

 which solidify after flowing in molten streams from visible 

 vents ; and by analogy with the crystallization of mineral 

 substances artificially melted and allowed to cool. The 

 granite is therefore regarded as an igneous rock ; a rock 

 which has been at one time molten from heat. 



The granite occupies a belt across the Island, enclosed 

 on the north and south by rocks of other kinds. Isolated 

 areas of granite are found eastward from Bass Harbor 

 Head, and at some other points. Descend the mountain 

 slopes to the lower ground, and although much of the 

 surface is covered with drift, the observer will sooner or 

 later meet with rocks of quite different appearance. At 

 first, these are seen as isolated angular fragments of 

 various kinds and sizes included in the granite ; the frag- 

 ments then become more frequent, as in the wonderful 

 display at Hunters Beach Head ; further on, the granite 

 is found penetrating long, relatively narrow crevices in 

 the other rocks, as on Sutton Island ; and at last the 

 granite ceases entirely, and the surface is occupied, when- 

 ever its rocky floor can be seen, only by rocks like those 

 first seen as fragments enclosed in the granite. Near the 

 margin of its area, the granite is finer textured than 

 further within its mass. This indicates that, when it 

 cooled from fusion, the margin cooled faster than the 

 interior ; for it is the habit of rocks when crystallizing 

 from a melted state to develop only smaller crystals and 



