THE DISTRIBUTION OF ANCIENT VOLCANIC ROCKS. 23 



structure, etc., in great perfection, although all trace of the 

 original glass has long since disappeared. The rocks collected 

 by Professor Bayley on the north side of Vinal Haven and on 

 the opposite shore west of North Haven are, according to his 

 field observations, all surface flows or tuffs. Of the nine speci- 

 mens kindly submitted to me for examination by Professor 

 Bayley, one is a medium grained microgranite and all the others 



Fig. I. 

 Fig. I. Devitrified glass-breccia from north side of Vinal Haven, Penobscot Bay, 

 Me. Magnified six times. 



are devitrified glassy rocks, which were once either obsidians, 

 glass breccias, or tuffs. No. 94 is a banded flow-felsite, a devit- 

 rified glass with narrow chains of spherulites. No. 100 is a 

 devitrified obsidian containing delicate flow-lines produced by 

 trichites, some zircon crystals, and spherulitic bands in which 

 epidote has been secondarily produced. No. 126 is a pale gray 

 felsite containing large round nodules which may be spherulites. 

 Under the microscope it shows a pronounced perlitic structure. 

 These rocks contain spherulitic structures which are not devitri- 

 fication products but original, if we may judge from their abso- 

 lute identity with similar structures in the glassy rocks from 

 Obsidian Cliff. The other five specimens are fine grained vol- 



