GEOLOGY OF MOUNT DESERT. 55 



they possessed when the felsites overflowed. It is there- 

 fore probable that the diorite is younger than the felsite. 

 At certain points in Northwest Cove, on the western coast, 

 the diorite is of two kinds ; the finer textured masses 

 being cut by those of coarser texture, and thus indicating 

 two periods of intrusion of this rock. 



This general survey of the older rocks may now be 

 summarized. The metamorphic schists seem to be the 

 most ancient, and it is probable that a long unrecorded 

 time elapsed after their deposition before the next series 

 was formed. Then comes a variety of unaltered sedimen- 

 tary rocks, to whose accumulation a long time must have 

 been devoted, and whose history was diversified by much 

 volcanic action. The geological date of these rocks can- 

 not be affirmed ; but, judging by analogy with similar rocks 

 along the New England coast, it was probably Cambrian, 

 a very ancient time division of geological history. How 

 long the conditions of deposition prevailed, and how great 

 a thickness of deposits was formed before their subsequent 

 destruction began, no one can now learn ; but we shall see 

 reason to believe that the existing amount of bedded rocks 

 is probably only a small share of what once existed in this 

 region. At some part of the time, when the accumulation 

 of the bedded series had reached a considerable volume 

 above the present surface, the intrusions of diorite took 

 place within the mass ; and again, at a still later time, 

 came the great granitic intrusion ; thus leading us to 

 the undated epoch with which this account of the rocks 

 began. 



THE POST-GRANITIC ROCKS. 



The only indurated rocks now recognized as of later 

 date than the granite are the trap dikes, by which all the 

 other rocks of the Island are traversed at one place or 



