220 SIR ARCHIBALD GEIKIE ON THE BASIC AND [May 1 894, 



These marginal structures are exhibited along the whole length 

 of the junction-line of the granophyre with the basic rocks of the 

 ridge from the western slopes of Meall Dearg southward. The 

 granophyre, as it approaches that junction-line, becomes fine- 

 grained or felsitic in texture, showing here and there abundant 

 spherulites ranged in rows along the lines of flow- structure, which 

 are sometimes remarkably well developed and run parallel with the 

 edge of the rock. In the ravine on the west side of Meall Dearg, 

 where the vertical line of contact between the basic and acid rocks 

 has been so well exposed, the perpendicular rows of spherulites run 

 up the bare faces of granophyre. 



It is important to observe that, at this locality as elsewhere, 

 no dependence whatever can be found between these marginal 

 structures in the granophyre mass and the various rocks of the 

 ridge against which they abut. The spherulites, for instance, are 

 to be seen just as well in the acid rock where it impinges on 

 the agglomerate as where it lies next to coarse massive gabbro. 

 There is, indeed, nothing unusual in this feature ; on the contrary, 

 it is exactly what any geologist acquainted with the behaviour of 

 intrusive bosses would have expected. Prof. Judd speaks of having 

 observed the spherulitic structure and felsitic texture " at one or 

 two points" along the junction -line of the basic and acid rocks, but 

 he makes no further reference to this observation. He apparently 

 groups these marginal structures with those of his ' inclusions,' 

 regarding them as due not to the more rapid cooling of the outer 

 shell of the granophyre, but to the re-fusion of that rock from the 

 protrusion of the gabbro through it. Whether fusion on so large 

 a scale could have been effected in a solid mass of granite by the 

 breaking through it of a continuous body of gabbro is obviously open 

 to grave question. To assert that structures which are common 

 characteristics of the marginal portions of bosses, sills, and dykes 

 are in this instance produced by re-fusion, and thus that what by 

 the ordinary laws of evidence would be set down as the older rock 

 is here really the newer, surely demands specially cogent and 

 copious proof. But even if we grant that a large mass of gabbro 

 disrupting a previously solidified granite might possibly induce upon 

 it these marginal structures, is it conceivable that a complex 

 assemblage of basic rocks, successively injected in thin sills and 

 narrow dykes through each other, such as I have shown to con- 

 stitute the ridge north of Druim an Eidhne, could have produced such 

 effects ? Is it to be supposed, too, that the agglomerate exercised 

 the same melting influence on the rock next to it, which, as I have 

 shown, presents just the same structures ? In short, even were 

 there no other evidence than this fine-grained felsitic aud spherulitic 

 margin, this, I submit, would be in itself sufficient to prove that 

 the granophyre has broken through the gabbro. 



The structures so well exhibited on the periphery of the grano- 

 phyre are not, however, confined to that part of the mass. On 

 the rocky slopes south of Meall Dearg, close to the edge of a gully 

 cut by the southern fork of the stream which drains that hillside, a 



