196 H. Workman — Calcite as a Prima)'// Constituent 



Biotitc, sparing^ fotind except in the limestones, in the most basic 

 differentiation products, and in the border acid zones, where it has 

 generally crystallized in ragged flakes later than felspar. Phlogopite is 

 not present except in blocks, not found in situ, seen on Langorsholmen 

 which came from the channel between the latter and Alno. 



Melanite or a titaniferous black garnet, abundant in all types either 

 in zoned rhomdodecahedra or in large irregular crystals, whose outline 

 is determined by the surrounding minerals. The zonal character is 

 roughly shown by the variation in colour from a deep black to 

 a brownish tint. It includes aegirine, calcite, nepheline, and sphene. 

 Thus the crystallization of the melanite extended over a long 

 period, beginning early and finishing late. Just such an occurrence is 

 described (2) (3) in the Borolanite, in Assynt, and in some of its more 

 basic associates, which resemble the Alno rocks in other particulars. 



Sphene, irregularly distributed and sometimes very abundant in fine 

 lozenge-shaped crystals ; also twinned and with inclusions of apatite, 

 calcite, and oegirine — in this latter case of comparatively late 

 formation. 



Fluor apatite, free from chlorine, exceedingly abundant. It occurs 

 as grains in the ground-mass and included in the silicates, and also 

 as prismatic crvstals arranged in most beautiful stellate rosettes, 

 Pis. XI and XII, Pigs. 2 and 3. 



Titaniferous magnetite, found mainly in types rich in ferro- 

 magnesian minerals. 



Olivine, confined to the basic and ultra-basic groups and to the 

 limestones. It occurs as fresh crystals, deep black in hand-specimen, 

 and also in all stages of serpentinization. 



The nepheline - syenites need no special description here. 

 A typical example is shown in PI. XI, Pig. 1. 



The limestones occur in two modes: either granular, when 

 a distinct banding, is seen, or pegmatitic. All the minerals of the 

 nepheline - syenites, except cancrinite, are found in them, and in 

 addition the rarer minerals pyrochlor, knoppite, zircon, and 

 munganophyllite ; these latter are found in one locality only. The 

 metamorphic contact minerals such as tremolite, diopside, and 

 forsterite, characteristic of impure sedimentary limestones and dolo- 

 mites, are always absent. Wollastonite has only been recorded by 

 Tdrnebohm in an isolated instance, and phlogopite seems to be 

 restricted to the loose blocks mentioned above. Where the limestone 

 is free from normal igneous accessory minerals it is exceedingly pure. 

 Analysis has shown that it then consists of 98 per cent, of calcite. 

 The minerals most commonly associated with calcite, where the latter 

 is abundant, are biotite, apatite, titanomagnetite, olivine, felspar, and 

 segirine-augite. Of these apatite is the commonest and in parts 

 makes up as much as 20 per cent, of the rock. Its characteristic 

 radial development is seen in PI. XI, Pig. 2, and PI. XII, Pig. 3. 

 In granular form it often occurs as numerous inclusions in a frame- 

 work of nepheline and pyroxene. The structure in the limestones 

 is generally hypidiomorphic, but in the pegmatites very beautiful 



