270 The Ametican Geologist. November, 1900 
I. The first method of alteration commences by an open- 
ing of the cleavage lines or a dissolving away of the material 
along cleavage lines ; but this stage is often absent. It is only 
rarely, and then only in very small areas, that the transformed 
feldspar is carried away, and the empty cleavage left; usually 
the material remains in place as some zeolite of fibrous habit. 
Next very fine particles appear which are opaque and black 
by transmitted light, and red by reflected Hght; they are 
doubtless hematite. As long as these changes are limited in 
amount they are also limited strictly to the cleavage lines, but 
when the transformation proceeds further the zeolite material 
begins to spread roughly at right angles to the cleavages, first 
sending out numerous narrow branches which soon connect 
the long cleavage lines by many perpendicular cross lines, 
thus forming an irregular quadrillage. The irregularity con- 
sists mainly in the fact that while one system of lines parallel 
to the cleavages is straight and continuous, the other system 
perpendicular to the cleavages is made up of lines very dis- 
continuous, the same line only rarely crossing a cleavage line ; 
at the same time these lines vary occasionally from the j3er- 
pcndicular and may even be curved. Hematite particles are 
rare along these lines. 
After this stage the zeolitic material spreads in a manner 
wholly irregular and thus forms masses of shapeless outline — 
patches scattered through the feldspar. At the same time the 
hematite becomes more abundant and forms little masses no 
longer limited to the cleavages, but occurring indiscriminately 
here and there. 
This method of alteration has never been observed tO' 
reach its fullest completion, and transform large areas of feld- 
spar into zeolites, without the presence of the second method 
working at the same time. 
II. The latter is much more rapid and irregular in its de- 
velopment; it follows no crystallographic directions, but oc- 
curs along the fracture lines which are always common in alt- 
ered areas — doubtless because alteration has been much facil- 
itated by the presence of these fractures and has thus devel- 
oped itself with especial ease wherever they were present. 
The fractures are sometimes accompanied by a very slight 
change in extinction in various parts. This method of altera- 
