120 ROSENBUSCH : METAMORPHOSED SKIDDAW SLATES. 
lie pretty regularly in rows, and this circumstance in conjunction 
with a stratiform alternation of the quartz and other constituents, 
gives the rock a banded appearance. The rock consists in this stage 
of a not quite microscopically fine-grained mixture of brown, strongly 
pleochroic magnesia-mica, colourless potash-mica, and quartz. The 
aaa. substance is no longer scattered as a fine dust through 
e whole mass, but clustered together in large patches. As an 
seth, tourmaline is not very rare, and sometimes in similar 
quantity, i.e., in sparse granules or little crystals, occurs andalusite ; 
more commonly pyrites. The rock is thus a true spotted or knotted 
andalusites, or that from the mechanical mixture which constitutes 
them andalusite is subsequently developed, the microscopic analysis 
gives not the slightest support. The crystal-sections in the Chias- 
tolite-slate have absolutely nothing in common with the knots in the 
tolite-crystals are not always clearly distinguished from one another, 
and so it is very difficult to obtain a clear picture of the progress of 
the metamorphism: sometimes the formation of chiastolite crystals 
in unaltered slates, sometimes the formation of knots is indicated as 
the se stage. Still, I think, in spite of the opposite statement in the 
‘Summary,’ I may venture the idea, based chiefly on my own 
Spi cikis that the development of chiastolites in the still 
unaltered slate here as elsewhere precedes the formation of knots, 
where the latter goes hand in hand with a crystallisation of the 
material of the slate. Thus the Chiastolite-slate would be an 
equivalent of the knotted-clay-slate (Anotenthonschiefer), and the 
knotted-mica-schist would follow this. 
It is absolutely unintelligible to me how Ward (l.c. p. 4) can give 
the absence of pleochroism in support of the suggestion of andalusite. 
Apparently there exists here a confusion with the small laths 0 
colourless potash-mica, and Ward has not seen the andalusite, which 
one can identify simply by its pleochroism among the colourless 
minerals of the rhombic system. No more can I imagine what the 
author has meant by the following passage on the same page: 
‘When viewed with polarized light, most of them [the spots] 
oer? exhibit shades of colour arranged i in the form of a cross, as 
shown in fig. 3, and there seems to be little doubt that the spots are 
AR oes chiastolite crystals.’ The appearance here described 
is here and there visible in the specimens lying before me too, and 
simply depends upon a a radial grouping of the mica-flakes. 
N Naturalist, 
