584 PROCEEDINGS OF THE PHILADELPHIA MEETING 



(3.) Highly metamorphosed slates and flags with bedded felsites between 



them, occurring at Suttons and Cranberry islands and along the 



south shore. 

 (4.) Similar flags, slates, and granite with magnesian rocks on the north 



shore from Rodicks cove to the " Ovens." 

 (5.) Stratified volcanic breccias, porphyries, and ash beds found only south 



of Southwest harbor. 



II. (1.) The great granite dike forming the massive of the several elevations of 

 mountains and mounts traversing the island in a direction west 25 

 degrees south, together with smaller connected and disconnected 

 intrusions. 



(2.) The felsite porphyry dikes. 



(3.) Dense dark colored "dike stones" which occupy the entire area of the 

 main and outlying islands. They are much narrower, and so 

 numerous that any line of 1,000 feet east and west will cut several 

 of them. 



(4.) A rare greenish trap. These several dikes have the most various 

 strikes. Nine-tenths of them are the ordinary dark colored trap- 

 pean materials common throughout the metamorphosed districts of 

 New England. The larger and more numerous dikes have a strike 

 of northeast and southwest, while the smaller number have direc- 

 tions about at right angles to this course. 



(5.) Short dikes of white quartz "which seem to have been injected in a 

 molten state and not deposited from solution in heated waters." 



Professor Shaler ascribes the isolation and lack of continuity of the sedimentary 

 rocks mentioned under I to causes which operated before they were divided by 

 the granites — in other words, by erosion previous to the appearance of the igneous 

 rocks. The interpenetration of the granite in minute threads proves that it must 

 have been very fluid and consequently encased in rock. This conclusion draws 

 the other that a vast but unknown amount of erosion must have taken place since 

 the injection of the granite. 



Essentially, Professor Davis agrees with Professor Shaler as to the probable rel- 

 ative age of the schists and flags and the likelihood that these sedimentary rocks 

 represent the Cambrian or earlier. He recognizes, however, that all the rocks of 

 the island are traversed in one place or another by the trap dikes. 



It is worthy of note that on the south slope of Green mountain, about half a mile 

 from the summit, is a knob or lesser summit, which, in a section made over the 

 mountain from north to south is the first exhibition of a massive dike of basalt. 

 Contacts with the pegmatite or granite are numerous, and the vent through which 

 this mass of basic igneous rock reached the present surface seems to lie wholly 

 within the granite mass. Moreover, the filaments of this basalt cut, intersect, and 

 inclose the granite exactly as the granite in other localities is seen to cut, inter- 

 penetrate, and inclose fragments of the elastics through which it has passed. 



Thin-sections of these rocks have been kindly made for me by Dr H. W. Wiley, 

 director of the Chemical Bureau of the Department of Agriculture, and are here 

 submitted for the inspection of the petrographers. 



