175 



The replacement of the original felspar by a felspar-mosaic is illustrated 

 in fiy$. 22 find 23. The photographs from which the figures have been 

 prepared were taken under crossed nicols. In fiy. 22 the greater portion of 

 the field is occupied by the original felspar ; it is, however, traversed by a 

 band along which the mosaic structure has been developed. The individual 

 grains of the mosaic are for the most part imtwiiined. In Jig. 23 a much 

 larger portion of the original felspar has been replaced by the mosaic. 

 Traces of the original individual may, however, be followed across the area 

 represented in the figure by the parallelism in the twin lamella?. 



Fig. 23. 



