Re 
86 : » Pentti Eskola. (CXTIF SER 
clase. The pyroxene, when fresh enough to allow of optical 
study, is pale green aegirite-augite showing faint pleochroism 
and the angle c:a =737". All these minerals seem to be 
nearly identical with those in the sviatonossite. The garnet, 
however, is richer in titanium (see analysis III p. 55). 
Another difference is the general occurrence of biotite in 
the borolanites, probably owing to the deficiency of silica 
which also appears in the presence of lenads. MNephelite 
and its alteration products are regular constituents in most 
types, and some of them have white spots which have been 
interpreted as pseudomorphs after leucite. 
The chemical nature of the borolanite-rocks is largely 
masked by a thorough alteration of most of their minerals, 
probably under the »postvolcanic» period of the laccolith. 
As products: of decomposition appear micaceous minerals 
and »chlorite» -and especially zeolite-minerals. Nephelite in 
most cases is said to be entirely replaced by »pinitic mica»: 
It is therefore natural that the analyses do not give any 
true idea of the composition of the rocks. They have almost 
certainly been enriched in alumina; the corundum appearing 
in the norm of analysis VII is due to such an alteration, 
and so is the large amount of normative anorthite in all of 
them. Analysis X giving normative leucite is suggestive of the 
probable original content of that mineral, though the de- 
composition may also very well have caused an enrichment 
in the potash, as must be the case when nephelite is converted 
into mica. The normative wollastonite is contained in the 
melanite which is abundant and greatly unaltered in the 
borolanite. On the whole, it may be coneluded from the 
primary mineral composition of the Borolanites that their 
chemical composition would be much more like that of the 
sviatonossite if they were not decomposed, and among the = 
types having excessive silica one could probably find chemi- 
cally identical specimens of both rocks. 
The leucite-tephrite and some other leucite- 
bearing rocks are also characterized by simultaneous high" 
percentages of lime and alkalies, and their bulk composition 
may often be very like that of some malignite or borolanite. 
