BY W. H. TWELVETREES AND W. F. PETTBRD, 21 



Microscojiical characters. 



Essentially dioritic. What is remarkable is the decided 

 'dominance of hornblende as a constituent of the rock. 

 This mineral forms irregular hypidiomorphic plates, Often 

 reduced to a granular condition by dynamo-metamorphism. 

 It is intergrown with biotite, which often accumulates in 

 nests or aggregations of flakes. In the hornblende 

 c :C = about 14°. a pale yellowish green, 6 dark brown 

 green, c dark green. The biotite is the ordinary type. 

 Some of the felspars are larger than the rest, and these 

 are hypidiomorphic, while the smaller felspars of the 

 pseuclo-groundmass are allotriomorphic. Many felspars 

 are simply twinned on the Carlsbad plan, others albite 

 twinned. A good deal of the felspar appears to be labra- 

 dorite. The other constituents are apatite, sphene, quartz, 

 and pale augite in small quantities. 



The predominance of hornblende and the allotrio- 

 morphic felspars may be looked upon as exceptional for 

 diorite pure and simple. Our rock is certainly dioritic, 

 but its structure is rather aplitic than plutonic, conse- 

 quently belonging to the dyke series of diorites. It is 

 somewhat schistose in thin section, though not so macro- 

 scopically. It seems allied to the plagioclase hornblende 

 aplites described by Osann from the Odenwald, and called 

 by him malchite. Of our slides of the malchitic rocks — 

 orbite, luciite, and malchite — luciite most resembles ours, 

 but we do not grasp the essential distinctions intended to 

 be expressed by these divisions. The quartz in our variety 

 is present in very small quantity. 



It is not easy to understand the occurrence of a dioritic 

 rock in this plexus of trachytes ; and, in view of the fact 

 that Professor Rosenbusch in his recent " Elements of 

 Petrology " (p. 135) has stated that diorites not only have 

 no chemical or mineralogical relationship with the alkali 

 syenites, but have never been found integrally associated 

 with them, we would reserve the present peculiar rock 

 for the additional examination which it merits and 

 .requires. 



DISTRICT OF LITTLE OYSTER COVE. 

 Alkali Syenite, with accessory Elaeolite. 



This is represented by a piece of rock from Mr. Innes's 

 property, a mile back from Oyster Cove. We have not 

 been able to examine the occurrence in situ, and from the 

 small quantity of material at our disposal we can only 

 give a general account of the characters of the rock. 



