be determined by it ; there are, however, also parts in which 

 the alteration has been so complete as to make a connection 

 with the earlier state impossible. 



Both the localities of the ilvaite are found close to the 

 borders of the more recent plutonic territory mentioned above, 

 but in neither of the places it reaches quite to the outermost 

 parts. At the Kangerdluarsuk-Fjord the ilvaite is only found on 

 a small tract exclusively inside of the territory of the augite- 

 syenite. At Siorarsuit, on the other hand, it is not only found 

 in this rock, but also in the sodalite-syenite and the lujavrite; 

 and further in a rock, which is perhaps transformed foyaite. 

 The extent of the occurrence of the ilvaite may be estimated 

 to about 1 km. in the direction W.-E., while in the direction 

 N.-S. it is not more than half of this extent. West of the 

 augite-syenite quartzy sand-stone is found at Siorarsuit, which, 

 however, does not seem at all to have been influenced by the 

 process that has formed the ilvaite. 



Crystalline form. 



In the following treatise the ilvaite of each of the mentioned 

 rocks has, for the sake of clearness, been treated separately, 

 although it may in each of these rocks show considerably 

 greater reciprocal differences. As a base for the setting up of 

 types, 1 have only made use of such characters as are found 

 to a greater or smaller extent in all crystals of the rock; as 

 a rule each of the pieces brought home contains only crystals 

 of one type. In a few cases it has been possible to connect 

 the occurrence of a certain type with alterations of the com- 

 binations of minerals around it; but in most cases, and espe- 

 cially with regard to all the types that I have had no occasion 

 to see in nature myself, it has not been possible to do so. 

 An examination of the different forms of crystals of albite that 

 are everywhere, without any single exception, found together 



