364 Geological Survey of the Island of Jersey. 



composition, being, for the most part, full of cavities, which 

 contain pulverulent black oxide of manganese, 32. This 

 mineral penetrates it in every direction, giving it, when acted 

 upon by the weather, a constant tendency to separate into 

 small shapeless pieces. 



Carbonate of lime (nearly the only hitherto observed ap- 

 pearance of it in the island) is also found in this rock in small 

 and irregular portions. 29, 30, and 31, shew the green por- 

 phyry in a state of incipient decomposition, after an exposure 

 of a few years. 37 is the same rock, containing iron pyrites, 

 in the neighbourhood of a mineral water, z, in St. Saviour's 

 parish. 



At x and y it passes into 36 and 33 respectively. 



36 is found at u in the Trinity Valley, at V in Anne Port, at 

 Bonne-nuit bay, and Havre Giffard. 



33. A very abundant rock extending over the yellow space, 

 dashed with yellow : it decomposes, especially when just under 

 the surface of the ground, as in specimens 34 and 35. It often 

 presents a white striated appearance when superficially decom- 

 posed, thereby shewing a near relationship to 10. 



10. The structure of this rock is best exposed on the sea- 

 coast, where it appears as waved and striped, as if it had, in 

 its soft state, been somewhat irregularly worked about. 



It is pervaded by a large bed of argillaceous schist at Havre 

 Giffard, and at the bay east of Belle Hougue, marked y (No. 11). 

 When underground, but near the surface, the moisture decom- 

 poses it into its constituent and irregular laminae, which crumble 

 with great ease at the touch, and which become white when 

 exposed to the sun in this state. 



A reniform variety of felspar, with concentric coatings 

 (No. 12), is found in small irregular masses among the hollows 

 of this rock in St. Catherine's Bay. 



3 and 2. From Boulay Bay, where they abound. 



4. I am uncertain as to the absolute locality of this rock in 



