54 KOTO : NOTES ox THE GEOLOGY 



I). AMPHIBOLIZED GAB URO. 



A dark-greyisli, coarse rock of gabbroitic aspect, in wliicli 

 a cleavable hornblende lies after the manner of plutouics, and 

 a plagioclase is moulded upon the amphibole. Patches of 

 epidote and iron-pyrites complete the list of megascopic elements. 

 Under the microscope, the greenish-brown hornblende is for the 

 greater part altered into a nearly isotropic lamellse of chlorite, 

 calci te-films, and common epidote. The hornblende has been so 

 highly altered that the original substance remains but in few 

 stripes. The ^/6r^ioc/«st;-anhedra possess only a few twinned 

 lamella?, besides the Carlsbad type of twins. Suitable section 

 could not be found for ascertaining the nature of the plagioclase. 

 The general deep-greyish appearance of the felspar is due to 

 the presence of a penuine-like chlorite in the fissure of it. Com- 

 mon epidote occupies the place of the felspar and hornblende 

 in rugged plate. Crystalloid of apatite, full of air-pores, was only 

 once observed. 



I conjecture this rock to be a metagabhro, though a diallage- 

 like augite was never seen in my slides. This gabbroitic mass 

 probably makes the foundation of the island, and crops out on the 

 ivest coast, together Avitli the Apoandesite and Serpentine. 



E. SERPENTINE. 



Associated with the above rock, there occurs a Serpentine 

 which is yellowish-blue in its general appearance. Under the 

 microscope, the whole mass presents between crossed niçois a 

 beautiful lattice-work, Avhich is a characteristic feature of its having 

 being derived from an amphibole. There are found intermixed 

 with the Serpentine a little quantity of iron-ore. 



