318 MR. J. PAKK1NS0N ON THE ROCKS OP [May I9OO, 



intrusion which followed the porphyritic granite at Sorel Point. 

 Differences exist between them, but they are of a minor character. 

 Thus, the southern rocks contain micropegmatite ; in the northern 

 the intergrowth of quartz and felspar, where it occurs, is coarser 

 and of a less pronounced character. The southern rocks often 

 contain microporphyritic crystals of plagioclase ; in the northern 

 similar crystals, though frequent, escape notice among their 

 coarser- grained surroundings, also a considerable quantity of 

 plagioclase is intergrown with orthoclase. Both rocks, equally, 

 are deficient in hornblende and mica. The differences, then, on 

 the whole seem to be due rather to dissimilar conditions during 

 consolidation than to variety of composition. The specific gravity 

 is the same, namely, 2*59. 



(2) Relation of the Intrusive Acid Rock of the Western 

 to that of the Eastern District. 



It remains to be seen what relation the aplite of St. Elizabeth's 

 Castle bears to the granite of Greve d'Azette and St. Clement's 

 Bay. The westernmost limit at which the latter rock is found 

 is at the Bathing Pool between Le Dicq and Havre des Pas. On 

 the western side of the pool is the fine-grained red aplite ; on the 

 eastern is the granite, porphyritic, coarse, and enclosing numerous 

 dark fragments in various stages of absorption. The pool appears 

 to cover the junction of the two rocks, but a few crags out- 

 cropping on the southern side help us in forming a conclusion 

 as to their relations. These crags are clearly connected with 

 the porphyritic coarse granite, but vary considerably in com- 

 position and grain : an inconstancy that is largely due — as may be 

 clearly seen when on the spot — to absorption of basic material. 

 Crossing a short strip of sand, we come to the fine-grained aplite, 

 which here and there shows irregular streaks and veins containing 

 felspars quite § inch long, with some quantity of the dark minerals. 

 This weathers in a granular manner ; in other words, it presents a 

 great resemblance to the granitic rock in the immediate neighbour- 

 hood. 



On the eastern side of the pool the coarse granite is cut by 

 dykes of a red aplite, indistinguishable from that of Havre des Pas 

 and St. Elizabeth's Castle ; and these, as thin sections show, contain 

 occasionally some amount of basic material. Accordingly we 

 may conclude that the fine-grained aplite is younger than the 

 porphyritic granite, but that the difference in age is probably 

 not great. 



IV. Conclusions. 



Taking the rocks in order of age, we have: — 



(i) Firstly, a diabase, no doubt identical with that from the 

 north side of the island ; and associated with this, a rock composed 

 essentially cf granular hornblendes (differing from those of the 



