182 H. p. CUSHlX(i — AUdlTE-SYEXiTE (iXEISS NEAll LOON LAK K 



(iuartz occurs only sparing!}^ in this rock, though very quartzo.se 

 phases appear elsewhere in the Loon Lake vicinity. It is niainl}'' in 

 rather large, elongated, cylindrical individuals. The elongation seems 

 to he effected rather by solution and recrystallization than by crushing. 

 The individuals are either entire or made up of but few fragments, and 

 the line granulation which must have been produced by the crushing 

 process is nowhere in evi<lence. In the quartzose varieties the ferro- 

 magnesiau silicates recede with disai)pearance of the foliation, its place 

 being taken by a linear structure produced by the elongated quartzes. 



Some quartz is also found as inclusions in the feldspar, sometimes 

 rather numerousl}?' and with a tendency to micrographic growths. There 

 is also a small amount of interstitial quartz and orthoclase, which seems 

 secondary, 



Structure of the Rocks 



These rocks have a cataclastic structure. In the gneissoid rock, from 

 the third cut the granulation is pretty complete, but even there occa- 

 sional larger nuclei remain and show ixndulatory extinction. In the 

 coarser rock, from the first cut many such large fragments are found, 

 constituting more than half the rock. The Diana rock shows the struc- 

 ture even better. Precisely the same variations in degree of granulation 

 are to be found that the anorthosites exhibit, except for the lack of the 

 very coarse varieties in the syenite, such as make up a considerable part 

 of the anorthosite, but this is regarded as an original difference. In 

 addition to the cataclastic structure, the rock is nearly everywhere 

 foliated. 



v^llEMlOAXj j.!LN ALi I Sliife 

 TA BLE OF A NA L Y^E^S 



These syenites are so variable in minei'al content and their field rela- 

 tions to other rocks, which on the one hand are much more acid and on 

 the other more basic, and into which they apparently grade, are yet so 

 uncertain that a large amount of chemical work will be necessary in order 

 to full^^ elucidate the problems suggested. Only a beginning has been 

 made in this, which, however, suffices to show the character of the typical 

 rock and to permit of a certain amount of discussion and comparison 

 with other syenites. 



