102 Mr. Verchere 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. 



Fiff. 2. 



*o 



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 clue 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 made 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 



