54 AN OUTLINE OF THE 



but they are now steeply tilted to the south and deeply 

 worn away, so that the present surface in the Cranberry 

 Isles reveals what would have been originally almost a 

 vertical cross-section of the mass. Minute study may 

 discover interesting details of this chapter of the Island's 

 history ; but the record is fragmentary by reason of the 

 denudation that has swept much of the structure away, 

 and the submergence which has sunk a good part of the 

 remainder beneath the sea; and the remnant standing 

 above the present sea level is blurred over by the sheet of 

 glacial drift. Yet it is by putting together such imperfect 

 records as this that much of the geological history of the 

 world has been made out. A close study of the ancient 

 volcanic area in the southern part of Mount Desert would 

 doubtless well repay any one who can undertake it. 



Along the southern coast, east of Somes Sound, and at 

 various points on the western coast near Bartlett Island 

 Narrows, there is a dark-colored crystalline igneous rock, 

 known as diorite. It consists chiefly of hornblende and 

 a triclinic feldspar : the fine parallel lines on the cleavage 

 faces of the feldspar resulting from the twinning of crys- 

 tals can be easily seen with a hand lens, thus distinguishing 

 the triclinic feldspar of the diorite from the orthoclase 

 feldspar of the granite. The diorite is shown to be an 

 igneous rock by its structure, and by its intrusive relations 

 with other rocks, here and elsewhere. It cuts the lower 

 members of the stratified rocks near Northeast Harbor, 

 and it is frequently cut by or included in the granite ; 

 hence its age is intermediate between the ages of these 

 two ; but its relations to the volcanic felsites are not 

 yet surely determined. The felsites were contemporary 

 superficial extrusions upon certain members of the bedded 

 rocks, while the diorite presents only the features of a 

 deep intrusion, as if thrust in among the bedded rocks 

 after thay had accumulated in much greater mass than 



