180 Geological Society. 



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. Reasons 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 suggested 

 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 evi- 

 dence 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 Bay 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 orthoelases, plagioelase, 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, enclos- 

 ing among them numerous porphyritic orthoelases. Some move- 

 ment of the whole then appears to have taken place. 



