144 ANNALS NEW TORE ACADEMY OF SCIENCES 



interior of the prism has altered into masses of fibres of various orienta- 

 tion. 



The fibrous form of amphibole with low extinction angle is found in 

 numerous slides. In 115 and 118, it occurs in abimdance. Invasion of 

 garnet areas by amphibole is exhibited in a number of places. In 117. a 

 series of subspherical growths of amphibole, built up of plumose or ray- 

 like fibres, form a border between comparatively unaltered basalt and 

 transparent prehnite. Pyrite (or chalcopyrite) is in intimate inter- 

 growth. The pleochroism of the amphibole is much less marked in this 

 instance. Colors vary from yellow-green, parallel to Z, to very pale bluish 

 green or almost colorless at right angles to this. Elongation of fibres is 

 nearly parallel to Z as before. 



In the occurrences described, the very fibrous amphibole is found under 

 circumstances which show that its formation began in early stages of 

 alteration. Its range of stability appears to have been very extended, 

 however. It has been observed macroscopically in small acicular tufts or 

 sheaves resting upon the free crystal faces of heulandite, laumontite, 

 apophyllite and calcite, minerals of a late stage of alteration, in such 

 manner as to show later deposition. This inference is confirmed in the 

 slides. In 72, very fresh-looking groups are found in the midst of heulan- 

 dite, and in 51a, it is associated with heiilandite and calcite. In 120, a 

 group of fibres is surrounded by laumontite, and in 98 perfectly fresh 

 amphibole is surrounded by chabazite. Slide 129 shows a sheavelike 

 bundle of amphibole fibres in the midst of a large apophyllite crystal. In 

 the hand specimen of the last, similar tufts were seen, resting on a free 

 face of the apophyllite crystal. Slide 138 shows similar inclusions. In 

 a great many other slides (50, 50a, 62, 110), small quantities are found 

 in rarious associations. In some cases, there might be a question whether 

 the amphibole might not be a survival from a previous period of more 

 intense metamorphic activit}', but when it is seen macroscopically, resting 

 upon the faces of projecting euhedral crystals, the only inference which 

 appears justifiable is that it is of later formation. From these relations, 

 it appears probable that it continued stable at rather moderate tempera- 

 tures. There was, however, in the more open channels, a tendency toward 

 solution because of a diminution of iron and magnesia in the circulating 

 waters. In the places where it is found, there appears to be always some 

 comparatively unaltered basalt within a short distance, generally in the 

 same slide, but in the large masses of secondary minerals sometimes found 

 in the cavities in the trap sheet, there is no distinctly iron or magnesia 

 mineral left. The writer has seen masses a foot or more in size consisting 

 of pectolite, prehnite, natrolite and tliaumasite lying between the bowlder- 



