Cole — O.rigin of the Orbicular Granite of Mullaghderg. 149 



penetration. In an example described from the county of Down, 21 there can 

 be no doubt whatever that the porphyritic crystals of orthoclase and quartz 

 now found in the inclusions existed already as such in the granite that 

 melted these inclusions. The porphyritic crystals of orthoclase that distinguish 

 the granite of Shap Fell, in Westmorland, may similarly have become 

 imported into the included blocks, in which they are often conspicuous. At 

 the same time, something has passed out from these blocks, if only to make 

 way for these crystals, and for the permeating and unconsolidated granite 

 magma, which is now represented by quartz and smaller felspar crystals. 

 The inclusions have become granitised, because the surrounding matrix has 

 become enriched by basic matter. J. A. Phillips" figures crystals of orthoclase 

 extending from the Shap granite into the dark inclusions as evidence that 

 the two types of rock developed contemporaneously ; but the range of 

 subsequent observation prevents us from accepting this as a necessary con- 

 clusion. A. Harker and J. E. Marr, 23 who also regard the included blocks at 

 Shap as segregations, none the less point out that the orthoclase within them 

 has suffered from corrosion. While interaction took place between the 

 invading and the invaded matter, the surfaces of the inclusions became 

 rounded by solution and by outward diffusion of their substance, just as the 

 artificial angular inclusions of paraffin used by Benedicks and Tenow 

 (op. cit., 10, p. 108) became rounded in molten paraffin, when the addition of 

 resin to the latter allowed a sufficiently high temperature to be employed. 

 J. A. Phillips, 24 more than thirty years ago, recognised that a rounded form 

 might be imparted to an inclusion of foreign origin. 



Schwarz considers the case of felspathic molecules moving as such into the 

 invaded rock. Where, however, the inclusion resists permeation by the molten 

 magma as a whole, the transference of material probably occurs by a still 

 more subtle process of selection. Kurd Endell 25 has experimented with a lump 

 of limestone immersed in molten microcline, the inclusion being ultimately 

 converted into a yellow glass. He concludes from an analysis of this glass 

 that silica and soda may diffuse more rapidly than potash into a nucleus rich 

 in calcium. Where the softening is less, and even where the solid state is 

 maintained by an inclusion, a transference of matter from the surrounding 



21 G. A. J. Cole, "On Derived Crystals in the Basaltic Andesite of Glasdrumman 

 Port," Sci. Trans. R. Dublin Soc, vol. v (1804), p. 244. 



22 " Additional Note on Certain Inclusions in Granites," Quart. Journ. Geol. Soc. 

 London, vol. xxxviii (1882), p. 216. 



23 "The Shap Granite," ibid., vol. xlvii (1891), pp. 280 and 282. 



21 "On Concretionary Patches and Fragments of other Rocks contained in Granite," 

 Quart. Journ. Geol. Soc. London, vol. xxxvi (1880), p. 1. 



25 "Uber Diffusionserscheinungen in Silikatschmelzen bei hoheren Tempera turen," 

 Neues Jahrb. fur Min. &c, 1913 (2), p. 152. 



SCIENT. PEOO. E.D.S., VOL. XV., NO. XV. 2 B 



