376 Proceedings of the Cambridge Philosophical Society, 
Mr Whewell considers, in this paper, the formation of those 
macles of fluor which are usually brought from Aldstone Moor. 
Suppose two cubes of fluor, whose faces are parallel, to pene- 
trate each other, and suppose the interior cube to revolve round 
its diagonal through an angle of 60°, the angle of the second or 
parasite cube would then appear above the faces of the original 
cube or not, according to its position and magnitude. Mr 
Whewell then gives a formula, by which (when one crystal 
penetrates another, and by revolving round an axis through a 
determinate angle, makes its angles protrude above the faces of 
the crystal,) the position of the axis and angle through which 
it revolves may be determined by the measurement of the angles 
which the lines of section and faces of the parasite crystal make 
with the edges and faces of the original crystal. 
J. S. Henslow, Esq. M. A. of St John’s, commenced the read- 
ing of a paper on the Geology of Anglesea. 
The term Micaceous Schist would perhaps include the whole 
series of the oldest stratified rocks in Anglesea, which vary con- 
siderably in mineral character, but do not allow of separation 
into distinct formations. An exception is made in favour of a 
quartz-rock, which occurs in two localities in Holyhead Island. 
The real structure of this consists of a succession of contorted 
strata, rudely conformable to each other, a disposition which it 
is difficult to perceive, except in particular positions. There is 
a deceptive appearance resembling stratification, which arises 
from the parallelism preserved between the scales of mica dis- 
persed through the rock, causing an imperfect kind of cleavage, 
inclined at a considerable angle to the horizon. This appears 
to arise from some effort of crystallisation posterior to the ori- 
ginal depositions of the beds. The variety which succeeds this 
is a chlorite schist, which also appears, in certain situations, to 
consist of a certain succession of beds or strata, and to have ob- 
tained a laminated structure posterior to their deposition, dif- 
fering, however, from that of quartz-rock, in being parallel to 
the strata, arid consequently partaking of the contortions with 
which they are marked. Mica-slate and clay-slate are found 
associated with the chlorite-schist, and pass gradually into it. 
The chlorite-schist is associated in three or four places with 
heterogeneous materials, among which are jasper, dolomite, and 
