58 J. D. Dana—Decay of Quarizyte. 
the occurrence in it of a few large ragged cavities, and also of 
‘may have been the source of the crystals. So much of the 
quartzyte of Berkshire is of this feldspathic character that the 
supposition is reasonable ; but more facts are needed to sustain 
it. The feldspar (orthoclase) in the quartzyte of Cheshire and 
Washington (referred to in the former article) occurs both in 
fine grains and large. 
In the making of the pseudo-breccia the iron-colored bands 
are largely, as I stated, only stained quartzyte, the staining 
ue to the spreading of the oxide either side of a crack. 
This is well seen in thin sections. The crack is generally a 
wedging action, in most of the pseudo-breccia specimens I have 
collected, has been small, the pieces lying very nearly in place, 
notwithstanding the appearance of large displacement occa- ° 
sioned by the spread of the oxide. But in one of the speci- 
mens it is relatively large, some of the intervals between the 
pieces being a sixteenth of an inch wide. Where the width is 
greater than this, pieces of the quarzyte occur within the band 
of oxide that are results of the septation process. In the speci- 
men here referred to the oxide is oxide of manganese. In the 
wider openings it makes mammillary crusts over the opposite 
surface of the fissures, but extends across the fissure in some 
parts. There are no quartz incrustations. The opening of 
cracks by a wedging action from the slow depositing of a crys- 
tallizing mineral substance is finely illustrated in the well- 
known split and enlarged heads and stems of crinoids, from the 
Sub-carboniferous limestones of Indiana, Illinois, ete., in which 
the introduced mineral is quartz. The specimen here referred 
to (three-fourths of a pound in weight) is oue-sixth manganvse 
oxide, and consequently the oxide must have come from an 
external source. It was obtained at one of the Limonite ore- 
beds near the eastern foot of Mt. Washington, where manga- 
nese oxide was the chief product; and it was originally a mass 
of quartzyte in the drift; there is no quartzyte in place in the 
vicinity. It contains some scales of a silvery muscovite. 
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