Vol. 68.] PETEOLOGTCAL NOTES ON OTJERNSEY, ETC. 33 



removal. We think, however, that in the course of one visit or 

 another, we have seen all the principal varieties. 



They were grouped by Ansted as diorite and syenite, to which 

 a third, hornblende-gabbro, was added in the paper of 1884 ; 

 but we incidentally showed, in 1891, the close connexion of two 

 of them, and thus agree with Mr. Parkinson's^ conclusions that 

 these are the results of differentiation in a single magma. 



The diorite varies generally from a rather fine-grained rock, 

 which, when unweathered, is almost black, to one in which the 

 principal minerals are the size of a hemp-seed, or occasionally even 

 slightly larger : the latter kind being often a little richer in 

 felspar, which assumes a whitish colour from incipient decom- 

 position. A third variety,^ called ' birdseye ' by the quarrymen, 

 is more local. In this a number of roundish crystals of horn- 

 blende, commonly about 0*4 inch in diameter, are scattered in a , 

 matrix, usually more like that of the first-named variety, though 

 occasionally it becomes more felspathic and speckled in aspect. 

 A variety termed ' long grain ' exhibits a slight foliation, the horn- 

 blende crystals becoming rather elongated and assuming a rudely 

 parallel arrangement. This is sometimes streaked (as described in 

 1891) with the greyer kind.'' 



Occasionally the ' birdseye ' develops a very coarse structure. 

 We picked up some fragments exhibiting it on the floor of a pit 

 entered from Delancey Lane (north of St. Sampson's), and found 

 a remarkable case in certain skerries in Bellegreve Bay.^ Here a 

 streaky and ' spotty ' diorite (in close relation with both fairly 

 normal speckled and ' birdseye ' types) becomes locally so coarse 

 that the hornblende-crystals are sometimes nearly 2 inches long.' 

 Two extreme varieties also claim notice : the one, related to the 

 second of those mentioned above, but with much less hornblende 

 and more coarsely crystalline in structure, being generally con- 

 spicuous from some distance by its yellowish-white tint; the 

 other very dark in colour from the abundance of hornblende. Of 

 this we know only two instances, one at the bottom of the descent 

 into Bon Repos Bay, and another on the south-west side of Fort 

 Albert in Alderney. The latter^ one can be distinguished from 

 the more normal diorite by its blackness some hundreds of yards 

 away. Here, as a rule, it is simply, divided, but with a perfect 



^ Greol. Mag. dec. 5, vol. iv (1907) p. 74. 



2 It dominates, as shoATii in Mr. Hill's map, for about half a mile inland 

 from the coast between a little north of Vale Castle and a couple of furlono-s 

 south of Hougue a la Perre. 



3 Q. J. G. S. vol. slviii (1892) pp. 134-37. 



* Near an old battery and some 50 yards north of a low causev\'ay going 

 down to the sea. 



•' Even larger hornblende-crystals were obtained, prior to 1884, by Mr. Hill 

 in an otherwise normal ' birdseye ' from a quarry near Baubigny Mill. These 

 larger crystals often show a poecilitic structure (felspar). 



^ The microscopic structure is described in Q. J. Gr. S. vol. xlv (1889) p. 384. 

 The larger hornblende-crystals measure sometimes about half an inch in 

 diameter. 



Q. J. G. S. No. 269. d 



