of Igneous Hocks. 197 



graphic structure can be seen. The calcite shows clearly in the field, 

 where the nepheline and ferro-magnesians have weathered out from 

 it in ribs. At Langorsholmen near the junction with the typical 

 nepheline-syenite, very large crystals of brown mica two or tbree 

 inches in diameter are seen graphically intergrown with equally large 

 crystals of calcite. Under the microscope the simultaneous extinction 

 of the mica or the calcite, as the case may be, shows very well 

 that this is an intergrowth of individual crystals. As the structure 

 is on a fairly large scale, it is difficult to get a representative area 

 in the field of the microscope, but PI. XII, Fig. 3, shows a portion 

 of an intergrowth of this character. 



Olivine and calcite are also found in graphic intergrowth. In 

 hand-specimens the calcite then shows a curious schiller lustre, and 

 on careful examination a fine network of greenish-brown substance 

 is seen arranged along its cleavage directions. Under the microscope 

 this proves to be olivine, partly fresh but mostly serpentinized. 

 Plate XII, Pig. 4, shows such an intergrowth with magnetite in 

 addition. The latter is probably part of a single individual crystal; 

 the olivine and calcite certainly are. 



Xumerous inclusions of nepheline-syenite, two or three inches in 

 diameter up to about one foot, are found in the limestone. These 

 may be either magmatic segregations or else inclusions of nepheline- 

 syenite which have been melted and recrystallized by the limestone 

 in a magmatic condition. Around these inclusions fluidal banding is 

 seen gracefully following the contours of the included syenite. It 

 may be mentioned that the banded limestones of plutonic facies recall 

 in many features the banded gabbros and peridotites of Skye and 

 Hum. In fact, the description given by Sir Archibald Geikie and 

 Dr. Teall (4) of the origin of the banded gabbros of Skye could be 

 applied almost word for word to this case. It seems reasonable, 

 therefore, to regard the banding as a result of flow in a heterogeneous 

 magma. It can scarcely be regarded as a bedding structure, for 

 alternating with layers of almost pure calcite are others consisting 

 of aegirine, segirine-augite, biotite, nepheline, orthoclase, sphene 

 garnet and titano-magnetite. Black ' schlieren ', composed almost 

 entirely of dark constituents, occur every here and there. The 

 7ninerals interlock across the junctions of the bands, so that these 

 latter cannot be due to successive injections ; cataclastic structures 

 have not been observed, and there is no field evidence in favour of 

 dynamic action. 



There is, in addition to the nepheline-syenite, limestone and rocks 

 of intermediate composition, a great variety of basic differentiation 

 products consisting mainly of biotite, olivine, titaniferous magnetite, 

 apatite, calcite and a pleochroic augite (violet grey to greenish grey). 

 In places, workable titaniferous magnetite ore is associated with these 

 rocks. These differentiation products are present in quite subordinate 

 amounts, but are of great interest to the petrologist. They may be 

 paralleled with the ' Jacupirangite ' and other basic differentiation 

 products of an alkali rock series, in association with the titaniferous 

 magnetite of Brazil described by 0. A. Derby (5). The Jacupirangite 

 is, it will be remembered, composed of varying proportions of 



