440 Professor K. Busz — GranojjJiyre Dyke in Scotland. 



has often gone so far that nothing of the plagioclase material is left, 

 and only the still clear appearance of the centre of the crystals 

 indicates that originally plagioclase has been present. By this we 

 are led to the following consideration as regards the solidification 

 of the granophyre. The acid magma, when intruding into the 

 gabbro mass, has broken up a great quantity of the basic rock, and 

 being in a state of high temperature and great fluidity was able 

 to absorb a great part of the gabbro xenoliths. The plagioclase 

 xenocrysts had also been partly absorbed when the solidification 

 of the rock began to take place, the first separation being the 

 orthoclase, which crystallized in parallel intergrowth with what had 

 been left of the plagioclase crystals. Thus a very acid magma being 

 left, quartz crystallized next in small crystals, whereas the inter- 

 stitial orthoclase, filling np the spaces between the quartz individuals, 

 must be considered the last excretion. 



As further constituents of the granophyre, hornblende, pyroxene, 

 mica, and magnetite are to be mentioned. They are present in 

 considerable quantity, and disseminated throughout the whole 

 mass of the rock. They must, however, not be regarded as 

 originating from the granophyre magma, but are either xenocrysts of 

 the adjacent gabbro, or result from the absorption of basic material. 



Augite, occurring as diallage or as common augite, shows all 

 the same features as in the gabbro rock, with the difference that 

 the alteration here appears in a more advanced stage. Often the 

 whole of the augite or diallage crystal has been entirely altered into 

 green, uralitoid hornblende, whereas in other cases one or several 

 grains of the unaltered substance remain enclosed in the alteration 

 product. A decomposition of the uralite into a chloritic substance 

 can often be observed. 



There is also another variety of hornblende present, showing 

 a darker, brownish-green colour and also a more intense pleochroism. 

 It occurs in irregular patches and also in well-defined crystals, 

 which exhibit the characteristic cleavages and the outlines of the 

 hornblende prism. They are, therefore, not uralite, but must 

 be considered as separations, or recrystallizations, which can only 

 originate out of the granophyrio magma after it had been altered 

 by the absorption of the basic rock. This conclusion is corroborated 

 by the fact that such hornblende crj'stals can often be observed on 

 the junction line between the two rocks. 



The hornblende shows the peculiar colouring which can often be 

 observed in the variety named barkevikite, the outer part being 

 brownish-green, which gradually changes towards the centre into 

 reddish-brown. Biotite appears always in connection with hornblende. 



From this description the granophyre is seen to be very similar 

 to the one of Barnavave, in Ireland, which Professor Sollas described 

 as a diallage-amphibole-augite-granophyre. 



To sum up the results of the examination of the rocks from 

 Ardnamurchan — 



1. The gabbro is presumably a dyke-rock, belonging to the group 

 which has been termed beerbachite, and also partly a porphyritic 

 variety of the same— beerbachite-porphyry. 



