72 



Combination: è{010}, d{liO], t [ПО] , s{l20}, h[2\0}\ 

 w{ZOl}, P{lOl}, ö-{08l); besides all the forms enumerated in 

 the preceding type, may occur; but they play a quite insigni- 

 ficant part. 



The crystals have the most poorly developed faces of all the 

 types. The prismatic zone is exceedingly highly striated, still 

 more so than was the case in type XI ; the separate faces can 

 generally only be determined by means of their reflexes in the 

 goniometer. (t(081} is only very rarely developed in a tolerably 

 regular way; it is almost always combined with è(010] by 

 horizontal striae of combination reaching a very long way 

 down the latter plane. On the other hand P{lOl} and г()(301} 

 are rather well developed. 



Contrary to what is the case in all the other types, these 

 crystals are quite dull on the surface, frequently somewhat 

 iridescent; in the present case the possibility is absolutely 

 excluded that this nature of the faces may have been produced 

 by any process of disintegration, as has so often before been 

 shown to have been the case. 



Ilvaite from the Angite-syenite. 

 Type XVI. 

 The last form of ilvaite to be described, arises from trans- 

 formed augite-syenite. As before mentioned, this rock here, as 

 in many other places in this region, forms the outermost belt 

 of the more recent eruptive territory. Here at Siorarsuit the 

 breadth of this belt is only about 100 metres. To the west 

 the rock is bounded by sandstone, to the east by the trans- 

 formed foyaite mentioned above. The augite-syenite is upon 

 the whole only little transformed, and the ilvaite is only found 

 in the part nearest to the foyaite. Thus this is the case im- 

 mediately at the beach, where the syenite appears as quite low 

 rocks, while the before mentioned sorts of rocks in the terri- 



