"238 Reports and Proceedings — Geological Society of London. 



invaded the diabase, as well as a dioritic rock associated with it, 

 •streaking and veining them. Mixing took place as a result of such 

 intrusion, producing a composite rock characterized by elongated 

 hornblendes which occasionally attain a considerable size. Mica is 

 conspicuously absent. 



The intrusion of the granite following this is next described. 

 Here, as on the northern coast, local absorption of the older rock 

 has taken place. The resemblance between the mixed rocks is 

 •commented upon, and a parallel drawn between the basic and acid 

 rocks of Jersey and the eastern and northern coasts of Guernsey. 



Passing to the western district, the aplite of St. Elizabeth's 

 Castle is described, together with the melting and absorption which 

 have taken place as a consequence of this intrusion. Field evidence 

 indicates that this is later than any intrusion found in the eastern 

 district, though the difference in age is probably but slight ; thus 

 it bears out the results of work on the northern coast, where 

 the intrusion of an aplite was found to have followed that of 

 a porphyritic granite. Eeasons are given in the body of the 

 paper for believing that successive intrusions cannot be separated 

 the one from the other by hard-and-fast lines. Finally, it is 

 ■guo-crested that the various rocks considered are closely related, and 

 indeed form parts of one magma, the successive injections of which 

 became progressively more acid. 



3. "The Rocks of La Saline (Northern Jersey)." By John 

 Parkinson, Esq., F.G.S. 



The rocks of La Saline closely resemble those of Sorel Point, 

 about a mile to the west. A coarse porphyritic granite is found 

 in the upper part of the cliff which passes rapidly into an equally 

 coarse but redder rock, approaching an aplite in composition. The 

 latter occasionally contains mica in some quantity, and evidence 

 is given for concluding that this mineral has been produced by 

 the combination of the constituents of the augite of a dolerite, 

 through which the acid magma forced its way, and the felspathic 

 parts of the magma itself. This evidence is based (i) on the fact 

 that in one part of the Baj'^ a few outcrops of rock are found 

 identical with others from Sorel Point, which have been clearly 

 formed by the absorption of fragments of diabase (dolerite) by an 

 acid magma ; (ii) on the presence of fragment-like patches rich 

 in mica in the aplite itself; (iii) by the irregular distribution of this 

 mineral through the acid rock. A peculiar quartz-less rock is next 

 described containing large orthoclases, plagioclase, and chlorite : 

 it is concluded that the last-named mineral is derived from mica. 

 With some hesitation the structure of this rock is explained by 

 supposing that the intruding magma melted a mass of dolerite, 

 completely dissolved the felspar, and produced mica in the manner 

 indicated above ; and that as freedom of movement was not greatly 

 restricted, segregation of the basic elements followed, enclosing 

 among them numerous porphyritic orthoclases. Some movement 

 of the whole then appears to have taken place. 



I 



