137 
preserved in most cases; on the other hand observations show 
that the catapleiite has formed prior to the analcime, and the 
transformation of the eudialyte must accordingly have occurred 
before the cooling down of the rock!. 
Ægirine and arfvedsonite showing the typical characters? 
are present in great amounts. They occur in large allotrio- 
morphic anhedra, sometimes in parallel intergrowth with one 
another, filling the interspaces between the other minerals. The 
egirine is not only a primary constituent of the rock, but it is 
also found as an alteration product of arfvedsonite. In the 
latter case it occurs as very light coloured, fibrous aggregates 
and the majority of the fibres are parallel to the vertical axis 
of the original arfvedsonite. Interspersed in this egirine- 
aggregate numerous minute scales of a strongly pleochroic 
mineral showing deep reddish brown and light grayish brown 
absorption-tints are commonly found; the direction of maximum 
absorption in some sections is parallel to, and in others per- 
pendicular to, the direction of elongation of the scales; the 
mineral is probably hydrous iron oxide. 
This alteration of the arfvedsonite begins at the margin 
and proceeds along the cleavage craks; as a rule it affects only 
small portions of each arfvedsonite-anhedron. Locally, how- 
ever, the arfvedsonite has been completely converted into such 
fibrous aggregates of light-coloured or colourless egirine, and 
this will apply to all the arfvedsonite-bearing rocks of Ilimau- 
sak. Nice pseudomorphs of this kind have already been found by 
the earliest explorers of the [limausak region. The existence of 
the pseudomorphs has no doubt contributed to the uncertainty 
about the chemical composition of arfvedsonite which prevailed 
until J. Lorenzen cleared up the question”. 
1 The conversion of eudialyte into catapleiite has been described in ‘Med- 
delelser om Grenland’ XIV, р. 164 and PI. VI (1894). 
* Ibidem, р. 176 and р. 191. 
3 Meddelelser om Grønland II, 1881, р. 147, and Mineral. Magaz. У, р. 50. 
