Wadsworth.] 488 [November 7, 



greenish viriditic product arising from the alteration of the various 

 minerals of the rock and its presumed original base. There are 

 also other secondary products which will be spoken of later. The 

 feldspar as a rule shows the characters of basaltic plagioclase, but 

 presents a whitish fibrous and granular alteration (kaolin) in 

 places, as well as the viriditic product. The augite is cut by the 

 plagioclase and has a reddish brown color. Its shades, owing to its 

 dichroism, vary from a light brown to a yellowish brown. Its in- 

 clusions are principally magnetite and it is but little altered, the 

 product in that case being generally viriditic. 



The olivine is in irregular grains and crystals more or less fis- 

 sured and altered. Some show mainly a clear olivine mass with 

 little serpentinous alteration along the boundary and fissures, 

 while others are entirely changed to serpentine pseudomorphs 

 after the olivine. The serpentine is of a greenish, reddish brown, 

 or orange-yellow color, the latter predominating. This is some- 

 what dichroic, the shade varying. The olivine shows the usual 

 effect of the destructive action of the magma so commonly ob- 

 served in the olivine of basalts. Some orthoclase occurs, but this 

 appears to be entirely a secondary or alteration product in the 

 rock. Many clear spots of transparent opal (hyalite) occur, 

 while apatite needles are not uncommon. 



The magnetite is in grains and crystals sometimes cut by the 

 other minerals particularly the feldspar. It is also held in grains 

 in the olivine as well as in the augite and feldspar. The general 

 order of priority in the crystallization appears to be : magnetite, 

 olivine, feldspar, augite, followed by the various secondary prod- 

 ucts. 



This rock is regarded by me as having been originally identi- 

 cal with that forming modern basaltic dikes ; the present differ- 

 ence being entirely owing to secondary changes brought about 

 since the solidification of the rock. However in its present con- 

 dition it would ordinarily be called a melaphyr, and closely 

 resembles many of the melaphyrs of New England. 



A boulder found on the east side of the island on the top of a 

 hill at Lagg is a coarsely crystalline rock showing macroscopic 

 hornblende, feldspar, biotite, and epidote. 



Under the microscope it is seen to be composed of diallage 

 hornblende, feldspar, epidote, biotite, quartz, apatite, titaniferous 

 iron, chlorite, etc. The diallage is of a colorless, yellowish, green- 



