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Z HARKER: NORWEGIAN BOULDERS IN HOLDERNESS, 
times show a beautiful iridescence on their planes. ‘This, with the 
rather coarse texture of the rock and the tendency of the augite to 
assume a diallagic appearance, points to deep-seated consolidation 
of the rock-mass from which our boulders are derived. A micro- 
scopic examination of thin slices of the rock reveals some interesting 
features, especially the curious intergrowths of different kinds of 
felspar to form composite crystals. 
(II.) Rhomb-porphyries.—Another type of rock associated in its 
crystallised with an unusual habit, such that its outlines, as seen, for 
instance, upon the smooth surface of a boulder, have often the form 
ofarhomb. The crystals may be sharp-angled or rather rounded at 
the edges, and they frequently show irregular patches in their interior 
of different material, as if affected by corrosive action. They usually 
have a dark-grey colour. The fine-grained ground-mass in which 
these crystals are embedded is of a paler grey colour with a violet 
tone, but, when more weathered, it often assumes a reddish tint. It 
is chiefly felspathic, but a microscopic examination discovers other 
minerals, such as augite, apatite, and little flakes of dark mica. 
(II1.) Saussurite-Gabbros.—These rocks belong to another set 
of post-Silurian intrusions, found in western Norway and especially 
in the district around Bergen. They present considerable variations 
in appearance, fs speaking generally, they are evidently crystalline 
rocks of moderately fine to rather coarse texture, and in hand- 
decomposing felspar, never showing the bright cleavage-planes of the 
minerals in the augite-syenites, es the ponntely granular material 
rather vaguely denominated ‘saussurite.” By Reusch and other 
workers in Norway the rocks are conveniently termed saussurite- 
gabbros: the great alterations they have certainly undergone render 
their original character a matter of some doubt. The so-called 
saussurite is an aggregate of albite, epidote, zoisite, actinolite, etc., 
often requiring very thin slices and high magnifying powers to 
resolve it ; for the most part it must be formed by the destruction of 
a ‘necodedelapar The patches of hornblende are no doubt in 
great measure secondary too, and this is indicated in hand- 
specimens by their green colour and frequent fibrous structure. 
Several boulders of saussurite-gabbros have been collected from the 
beach between Bridlington and Flamborough. 
Naturalist, 
