102 Mr. Verchéere on the Geology of Kashmir, [No. 2, 
than the other. Two such plates are applied one against the other 
by their greatest surface, but one of the plates has (apparently) rotated 
half a turn, so that A of one plate is opposite B of the other. 
Fig. 2. 
This rotation is of course only apparent, but it appears to have taken 
place from the cleavage of the two plates being opposite, so that when 
we look at a section of the double crystal (fig. 2), one side presents 
the shining striped surface of a lamellar cleavage, whilst the other 
shows the dull rough surface of a fracture across the grain. This 
opposition of cleavage is probably due to a play of opposite electricity 
generated during crystallization, but it gives the idea of one of the 
plates having made half a turn before applying itself against its 
fellow. 
The perfect crystal is rarely seen; it is generally broken across, 
and the section (fig. 2) is conspicuous on the surface of the rock, 
so that, at first sight, one may fancy the crystals to be prisms, 
and a little trouble is necessary to understand the arrangement of the 
twin plates. This macle is therefore, to all appearance, a twin crystal 
of one of the numerous modifications of triclinic albite. 
By exposure to the atmosphere, the porphyry crumbles easily and 
falls to a coarse gravel which is soon converted into a very white 
sand. While the rock is still hard and sound, the large crystals 
