A CONTRIBUTION TO THE GEOLOGY OF SOUTHERN MAINE 551 



a width of thirty-five feet, and again on the western shore, where 

 it is still wider. On this latter exposure are glacial strias point- 

 ing N. io° W. The slightly inclined columnar structure is 

 evident here as elsewhere among the dikes. 



The subrang is a very common one, the most notable thing 

 about it being that within it are to be found four of the rock 

 types described by Mr. Lord from Monhegan Island. Of these, 

 two, malchite and beerbachite, are dikes ; two, gabbro and gabbro 

 diorite, are part of the older plutonic mass. The resemblance 

 to the Linekin diabase is chemical only, the mineralogy being 

 quite different. 



Microscopic Character. — The Linekin dike has a diabasic 

 texture, in which it is like the Sheepscot River dike just de- 

 scribed, but the resemblance is only of a very general nature. 

 The Linekin dike is porphyritic throughout, its principal 

 phenocryst being a broad plagioclase of the variety labradorite ; 

 other phenocrysts are augite and olivine. The augite is usually 

 surrounded by secondary hornblende. The ground-mass con- 

 sists of a network of lath-shaped plagioclases, in the interstices 

 of which are magnetite and augite. This dike is in all respects 

 similar in petrographic character to the one described by Dr. 

 Bascom, hence mineralogical details need not be repeated. 

 Identical with these is the long dike extending from Cabbage 

 Island to Five Islands. All are porphyritic olivine diabases, 

 with slight variations in coarseness of grain according to distance 

 from the edges. 



The southernmost of these east and west dikes, which out- 

 crops on the coast near Cape Newagen, shows considerable 

 metamorphism. The dike is the largest, measuring (by pacing) 

 one hundred and twenty feet in width. The original rock was 

 evidently identical with the others, but in places it has been so 

 crushed as to be practically a hornblende schist. Of the six 

 slides examined from different parts of this exposure all degrees 

 were to be observed between a slightly altered diabase with a 

 little green hornblende in addition to the minerals enumerated 

 above, to a true schist with hornblende and biotite as the only 

 ferro-magnesian minerals, and a schistose arrangement of these 

 leaves. The commonest type is a partly altered one containing 



