GEOLOGY OF MOUNT DESERT. 53 



includes their fragments along the southern coast ; hence, 

 like the greenish schists, they belong to the pre-granitic 

 series, hut at present it is only by inference that they are 

 regarded as younger than the schists, as already explained. 

 There may well be a considerable diversity of age among 

 these bedded rocks, yet to be discovered. 



The northern shore by the Ovens, the southwestern 

 extension of the Island, and several of the smaller islands 

 to the southeast, contain many exposures of old volcanic 

 rocks, known as felsites. They are of crystalline texture, 

 but much finer than the granite of the central belt, and 

 are often arranged, like modern lavas, in sheets or flows 

 parallel with the beds of the adjacent stratified sedimen- 

 tary rocks. They frequently possess a porphyritic structure ; 

 that is, small crystals of feldspar are disseminated through 

 the mass. Again, they have a banded structure, due to 

 flowing while molten ; and they are often broken or brec- 

 ciated, as if eruptive movement had continued after a part 

 of the mass had become solid. This structure is exhibited 

 on the eastern shore of Bass Harbor. Associated with the 

 denser masses are large fragmental and ash-like deposits, 

 as if formed by explosive eruptions from some neighboring 

 vent not now identifiable. Occasionally, dikes of felsite 

 are found cutting through the rocks of the bedded series. 

 Like the bedded rocks, they are cut by the granites, as 

 may be well seen east of Bass Harbor. Considering all 

 these features, it may be concluded that the felsites mark 

 a time of volcanic activity contemporaneous with a part of 

 the period during which the sedimentary series was formed. 

 The sandy or muddy sea bottom of that era must have 

 received, from time to time, flows of lava and showers 

 of ashes ; volcanic cones may have been built somewhere 

 in the neighborhood, although not a trace of tliem now 

 remains. While in process of accumulation, the bedded 

 rocks and the lava flows must have lain almost horizontal ; 



