296 NATURAL SCIENCE. j,,,^. 



produced. The microscope confirms these conclusions, and shows 

 that crystals have not only been rounded, but also reduced to the 

 condition of fine detritus. It is clear, therefore, that when the 

 ditroite was pressed upwards it consisted of a magma crowded with 

 already formed crystals. The author proposes the term protoclastic 

 for structures of the above kind, to distinguish them from the 

 cataclastic structures of Professor Kjerulf, which are due to the 

 deformation of a rock subsequent to final consolidation. 



In the immediate neighbourhood of the junction the laurvikite 

 has frequently been so broken up as to constitute a true breccia. 

 Lenses of laurvikite measuring from a half to one metre across, 

 sometimes smaller, however, and sometimes much larger, lie in a 

 matrix of ditroite. This remarkable complex appears to have been 

 formed in the following way. After the laurvikite had been consoli- 

 dated it became broken up into large and small fragments by a 

 renewal of the sinking process along the junction, and, at the same 

 time, the ditroite-magma, with its already formed crystals, was 

 intruded. The fragments of the laurvikite became rounded, and the 

 ditroite-magma caught up the detritus of the rock into which it was 

 injected. The fluidal structure in the ditroite is related to the 

 lenticles of laurvikite exactly in the same way as the fluidal 

 structure in a rhyolite is to the phenocrysts of felspar and quartz. 

 If we use the term rhyolite in its etymological sense, we may speak 

 of the complex rock here referred to as a rhyolitic breccia. There is 

 no reason to believe that any important interval of time elapsed 

 between the consolidation of the laurvikite and the intrusion of the 

 ditroite ; indeed, the occasional blending of the two rocks seems to 

 imply that the laurvikite had sometimes scarcely solidified before the 

 intrusion took place. The figures and descriptions of the author 

 show clearly that the phenomena here referred to are exactly similar 

 to those which may so often be seen in any extensive"gneissose region. 



In the same district pegmatitic injections may also be observed, 

 and this still further increases the resemblance to gneissose areas. 

 The author remarks that the phenomena above referred to can 

 scarcely be described by the term structure, inasmuch as we are here 

 deaUng with the mutual relations of rock-masses and not with the 

 mutual relations of minerals. He accordingly proposes that the term 

 architecture should be employed instead. 



The laurvikite, however, is not the only rock which occurs as 

 inclusions along the south-west margin of the plutonic area. Lenti- 

 cular masses of augite-porphyrite and rhomben-porphyry are also 

 found. In one locality fragments of augite-porphyrite are surrounded 

 partly by pegmatitic syenite and partly by a very dark variety o^ 

 schistose ditroite, which is termed by the author aegirine-ditroite- 

 schist. This basic ditroite forms a narrow zone, about half a metre 

 broad, round the lenticles of augite-porphyrite, and, therefore, 

 probably owes its basic character to the absorption of certain 



