444 MB. J. PARKINSON" ON AN INTRUSION OF aRANITE [Aug. 1 899, 



The following are the specific gravities, determined by a "Walker's 

 haiiamce, of some of the rocks described : — 



Aplite, specimen analysed, Sorel Point . . 2*59 



Porphyvitic granite, the earliest intrusion 260 



'Intermediate rock,' Sorel Point. Granite greatly- 

 predominating 2'61 



The same, more basic 2'67 



Diabase with material derived from granite (p. 439)... 2'84 

 Diabase with much less granitic material : silica- 

 percentage 51-13. 2-92 



Normal diabase 2-92 to 2-94 



YI. Comparison" of the Phenomena -with those observed in 

 OTHER Districts. 



It is scarce!}^ necessary to remark that the facts described in the 

 foregoing pages present great analogies with those recorded by 

 Prof. Sollas/ Mr. Harker,^ and Prof. Cole/ from the districts of 

 Barnavave, Strath, and Slieve Gallion respectively. But Mr. 

 Harker's remark, in his account of the granophyres of Strath, 

 .that ' the enclosed rock-fragments have not been derived from the 

 rocks which border the intrusions as seen in outcrop,'* points to 

 an important difference between the rocks which he describes and 

 those around Sorel Point. The regularity of distribution of the 

 ^absorbed material 'through the involving magma prior to the 

 consolidation of the latter in its present surroundings,' to which 

 he refers, is but occasionally found in these ISTorthern Jersey rocks, 

 .and then apparently to no great extent. The mineral changes 

 resulting from the amalgamation of two magmas show, as was to 

 be expected, both similar and dissimilar points. In La Plaine the 

 action on the felspars recalls to some extent the work of Back- 

 fStrom* on solution-spaces, formed in the foreign crystals of some 

 .dykes, rather than the alteration by injection with orthoclase and 

 quartz found in the bytownite of Barnavave; but the most striking 

 change has been concerned with the acid felspars, and not with the 

 basic ones of the older rock. The latter seem, not uncommonly, 

 to have been completely absorbed. 



A remarkable point of difference between the mixing at Strath 

 and that around Sorel Point consists in the absence of biotite, at the 

 former locality, as a product of the assimilation and recrystal- 

 lization of the augite. The mineral, however, occurs to a limited 

 extent in the immediate neighbourhood of fragments of basic lava 

 included in the gabbro of Carrock Pell.^ The restriction of this 

 constituent to a zone of a few feet around these inclusions, and the 

 fact that it is foreign to the normal gabbro implies, as Mr. Harker 

 points out, difficulties in the way of diffusion at the time when it 



1 Trans. Eoy. Irish Acad. vol. xxx (1894) p. 477. 



2 Quart. Journ. Geol. Soc. vol. lii (1896) p. 320. 



3 Sci. Trans. Eoy. Dub. Soc. ser. 2, vol. vi (1897) p. 213. 



* Bihang till K. Svenska Vet.-Akad. Handl. vol. xvi (1890-91) pt. ii, no. 1. 

 ^ Quart. Journ. Geol. Soc. vol. 1 (189^) p. 331. 



