274 



Canadian Record of Science. 



Augite-trachyte. A few of the hand specimens are typical 

 trachytes, showing beautiful flow structures, and consisting 

 essentially of orthoclase in two generations with augite as the 

 ferro-magnesian mineral. Titanite and magnetite are common 

 and persistent accessories, and brown garnets are usually pre- 

 sent. Whether these specimens of augite-trachyte were taken 

 from actual flows or whether they are merely rock fragments in 

 the breccias, is not clear from the data accompanying them. 

 A study of the breccias, however, shows that fragments of 

 augite-trachyte are quite common constituents of these pyro- 

 clastic rocks. The composition of the majority of the crystal 

 tuffs is also distinctly trachytic. 



Fig. 3. Analcite replaced by calcite ; crossed nicols : actual field is 2-5 mm. 

 The mineral with octaeroual outline in the centre of the fie'd is analcite, now 

 almost entirely replaced by calcite (while). 



Tivguaite. One hand specimen only in the collection 

 illustrates this type. It is a noncrystalline porphyritic rock 

 with phenocrycts of orthoclase (over an inch in diameter) and 

 augite set in a ground mass of orthoclase laths, nephelite and 

 many aegirite prisms and needles. This rock is interesting 



