from the Tilly Foster Iron Mine. 381 
eral was deposited : or that they were made during the change 
of the cubic mineral to serpentine. The former may have been 
the fact; and yet there is no trace of alteration in the chlorite 
crystals to show that they have passed through a time of ser- 
pentine deposition. 
4. Pseudomorphs after Chlorite. 
The change of the crystallizations of ripidolite to serpentine, 
in specimens from this locality, was early observed, in all its 
stages, by Professor Allen. My Breidenbaugh, in his account 
of the white serpentine, remarks that there is a gradual shading 
in the color of the ripidolite from bright green to pure white, 
and “in its texture from the foliation and transparency of the 
unchanged mineral to the compactness and opacity of the serpen- 
tine.” Specimens are common. Some are crystals, white and 
pearly, retaining the form of the ripidolite; others, aggregations 
of whitish folia, from fissures half an inch to three inches in 
width; others, white, grayish or greenish divergent fibrous 
masses, either large divergent groups, or stellated aggregations ; 
and+others are structureless white or greenish serpentine. 
of the specimens illustrate the progress of the change 
from chlorite to serpentine. The surface of a half-changed 
crystal is often marked with green and white, as represented 
in figures 6 and 7, plate v1; showing that, in the change, the 
cleavage-joints were a barrier to its progress; portions of the 
chlorite bounded by cleavage lines remaining still green, while 
other portions outside and beneath are wholly changed, on the 
principle illustrated in the cubic pseudomorphs. The green 
plates in the figure have the angles 60° and 120°, and perfectly 
even sides, 
When the change to serpentine is complete, there is often 
one or more of the outer folia on one side or another of the mass 
that still has some of the coior of the chlorite and removes all 
doubt as to the origin of the foliated mass. But from these 
there are gradations to other varieties, in which the foliaceous 
or radiated structure is wholly lost. 
The massive crystalline-granular chlorite of the ore-bed also 
occurs changed to serpentine; some of it retaining the granular 
structure, and other portions destitute of it. The color is often 
dark olive-green, while that of the crystals and foliated masses 
1s white or pale green. This fact suggests that this massive 
chlorite may 8 another species containing more iron. Breiden- 
ugh found in a massive chlorite of the mine 9°62 per cent of 
protoxide of iron, while the ripidolite crystal afforded only 5-29 
per cent; but his analysis leaves some doubt as to the nature 
of the former species. 
(To be continued. ) 
