320 ME. J. PARKINSON ON THE ROCKS OF [May 1900, 



19. The Bocks of La Saline (Northern Jersey). By John 

 Parkinson, Esq., F.G.S. (Eead March 7th, 1900.) 



The rocks of La Saline, an indentation of the larger St. John's Bay r 

 resemble very closely those from Sorel Point, a little less than a mile 

 to the west. Around the latter headland we find that a porphy- 

 ritic granite has forced its way into a diabase, shattering and 

 breaking it up, softening and locally melting it. Hence changes 

 can be readily traced in the acid magma, which is rendered basic,, 

 and in the diabase which is impregnated by it. M. Noury mentions 

 and maps 1 an outcrop of ' diorite ' at one point in the bay of La 

 Saline and surrounded by granite, but clear evidences of intrusion 

 are wanting. 



In a quarry on the cliff-top, and cropping out on a sloping path 

 which leads towards the eastern end of the bay, is a rather coarse 

 granite containing some quantity both of hornblende and mica, a 

 fair amount of quartz, and ]arge flesh-coloured orthoclases sometimes 

 £ inch long. At the eastern end, and forming the crags on the 

 shore, occurs a redder rock, less markedly porphyritic and inclining 

 as a rule towards an aplite, though occasionally some quantity of 

 black mica is present; its specific gravity is 2*60. At Sorel Point 2 

 two distinct intrusions of the acid magma are found : an earlier, 

 porphyritic, which has melted and partly incorporated fragments 

 of the diabase ; and a later, non-porphyritic aplite which took the 

 same course as did the first, but without its effect on the diabase. 

 These two have kept themselves distinct, though intimately asso- 

 ciated with each other. At La Saline both field and microscopic 

 examination suggest a passage, though perhaps a rapid one, between 

 the two rocks described above, which show a general analogy to 

 those from Sorel Point. Specimens distinct enough can be easily 

 found, but the study of a series tends to bridge the gap. 



Both contain large quartz-grains without a granophyric relation 

 to the felspars, and orthoclase with a microperthitic intergrowth. 

 The rock of the quarry possesses some quantity of free plagioclase, 

 but this is not absent from the red rock of the shore, where, however, 

 it is for the most part intergrown with orthoclase. Not unfrequently 

 the latter constituent is porphyritic. There is always a little black 

 mica, occasionally a considerable quantity, and herein lies the 

 interest. At one or two points just below high-water mark one finds 

 the red aplitic rock looking as though it had been irregularly 

 peppered, a peculiarity due to the presence of irregular and ill-defined 

 patches containing much black mica. This peppered appearance 

 catches the eye on the weathered surface of the rock, and the patches 

 join one with another in a kind of rough network. The rock is 

 rather more finely grained than usual. Close by, the quantity of 



1 * Geologie de Jersey ' 1886, p. 22. 



- Quart. Journ. Geol. Soc. vol. lv (1899) p. 430. 



