443 



Finally we can here also tix the attention to the fact, that the 

 RöNTGENograins of the apopliNllites of difFerent localities differ ^et 

 in their finer featnres, although they possess the same general 

 symmetry. 



§ 10. In onr opinion these investigations have decided without 

 any doubt between the two prevailing theories for the explanation 

 of the optical anouialies of apophyllite, in favour of Mallard's 

 hijpothesis'. not the tetragonal molecular structure, disturbed later by 

 internal stresses, must be considered as the primary state of the 

 mineral ; but this state corresponds to an originally inonocUnic 

 molecular ari-angement, which approaches very closely to a tetragonal 

 one, and which reaches its pseudo-tetragonal character by the 

 crossing and intergrowth of two such monosynimetric structures, 

 by means of polysynthetic lamellai' twinning, and a mutual [)enetration 

 in directions, which make an angle of 90° witii each other. 



POSTSCRIPT. 

 Finally we will use this opportunity, to add here again a con- 



Boracite at 300°. G. 



