334 ON A NEW STRUCTURE IN APOPHYLLITE, AND 



The tesselated Apophyllite, however, could not have been 

 formed by this process. It resembles more a work of art, in 

 which the artist has varied, not only the materials, but the laws 

 of their combination. 



A foundation appears to be first laid by means of an uni- 

 form homogeneous plate, the primitive form of which is pyra- 

 midal. A central pillar, whose section is a rectangular lozenge, 

 then rises perpendicularly from the base, and consists of simi- 

 lar particles. Round this pillar are placed new materials, in 

 the form of four trapezoidal solids, the primitive form of whose 

 particles is prismatic, and in these solids the lines of similar 

 properties are at right angles to each other. The crystal is 

 then made quadrangular by the application of four triangular 

 prisms of unusual acuteness. These nine solids, arranged in 

 this symmetrical manner, and joined by transparent veins, per- 

 forming the functions of a cement, are then surrounded by a 

 wall, composed of numerous films, deposited in succession, 

 and the whole of this singular assemblage is finally roofed in 

 by a plate exactly similar to that which formed its founda- 

 tion. 



The second variety of the Tesselated Apophyllite is still 

 more complicated. Possessing the different combinations of 

 the one which has just been described, it displays, in the di- 

 rection of the length of the prism, an organisation of the most 

 singular kind. Forms unknown in crystallography occupy its 

 central portion, and on each side of it particles of similar pro- 

 perties take their place, at similar distances, now forming a 

 zone of uniform polarising force, now another increasing to a 

 maximum, and now a third, descending in the scale by regu- 

 lar gradations The boundaries of these corresponding, though 

 distant zones, are marked with the greatest precision, and all 

 their parts as nicely adjusted, as if some skilful workman had 



selected 



