Cole — Origin of the Orbicular Granite of Mullaglidcrg . 151 



foreign inclusions, which were possibly sheets of sedimentary rock ? In that 

 case the change has been partly pseudomorphic, and the spherulitic form has 

 arisen, as at Mullaghderg, by the outward diffusion of material from the 

 original inclusions. 



The most interesting nucleus among those observed in the granite of 

 Mullaghderg is that shown below the letter F, on Plate IV, and, from 

 another section, in fig. 3. A long flake of biotite-sehist, perhaps originally 

 an amphibolite, 30 includes crystals of pink felspar, which in places seem, like 

 those of Barna, to be passing in from the similarly pink granite zone around. 

 Outside this granite-zone grey concentric zones of radially grouped soda- 

 lime felspar and magnetite occur, as in the ordinary spherulites; but the 

 external form has been controlled by the elongated nucleus. In the same 



Fig. 3. — Sketch of a partially granitised inclusion of schist in an elongated spherulite in the 

 granite of Mullaghderg, showing penetration by the zone of granite round it. The inner edge of 

 the radial region of the spherulite is indicated by the shading surrounding the granitic zone. Drawn 

 from polished surface. Natural size. 



plate a granitic nucleus is seen in the spherulite D, and this nucleus has 

 caused foundering and partial absorption of the concentric outer zones. 



It is not clear that the resorption of the spherulites, or the introduction 

 of the matter that has attacked and ultimately replaced many of their 

 original cores, is connected with the second intrusion of granite that formed 

 the subsequent veins. Such veins of pink aplite are well seen at H in 

 Plate V, and thin representatives of them traverse the main rock, the grey 

 radial zones, and the granitic nuclei of the spherulites. The formation of 

 the miniature cauldrons within the grey concentric and radial zones seems, 

 however, to have been contemporaneous with that of the grey zones. Their 

 contents were, however, reinforced from the still fluid magma round about the 

 spherulites after these zones had reached a fairly rigid state, and the molten 



30 Compare op. cit. (20), p. 185. 



2b 2 



