3G2 Watts and Newton — Rocks from Solomon Islands. 



II. — The Igneous Bodes. 



The igneous rocks collected by Lieut. Waugh appear, with two 

 probable exceptions, to be the products of recent volcanoes. Some 

 of them are anclesites corresponding very closely with those in the 

 large series deposited by Dr. Guppy in the British Museum and 

 described by the late Mr. T. Davies. By the kindness of Mr. 

 Fletcher and Mr. Prior, I have been allowed to look over the slides 

 of these rocks, and I desire to record my hearty thanks to these 

 gentlemen for the privilege accorded to me. Some others of the 

 rocks collected by Dr. Guppy are at present lodged at the Royal 

 College of Science, and they have been examined by Prof. Judd. 

 The latter has been so kind as to allow me to study his slides and 

 specimens. He has not only given me every possible facility for 

 working at them, but he allowed me to see his notes on the specimens, 

 for which I desire to thank him cordially. His specimens have, 

 however, little bearing on the present communication, except that he 

 recognized orthorhombic as well as monoclinic pyroxene in some of 

 the andesites. The plutonic rocks of Prof. Judd's collection are not 

 represented at all amongst those which have been submitted to me 

 from New Georgia and elsewhere. 



There are, however, in New Georgia a number of much more 

 basic rocks, porphyritic olivine-basalts, which, from the state of 

 preservation of their minerals, are almost certainly recent volcanic 

 products. No rocks quite like them are to be found in the British 

 Museum collection or in Prof. Judd's series. 



The occurrence of these two types of volcanic rocks in New 

 Georgia confirms Dr. Guppy's surmise that the island would be found 

 to be volcanic in structure. Although he was unable to visit it, he 

 inferred from its geographical position that it would be made up of 

 recent volcanic jDroducts, as it was situated on the important volcanic 

 line proceeding from Bougainville Island. 



The igneous rocks may be classed as follows : — 



(1) Porphyritic olivine-basalts with very little porphyritic felspar. 



(2) ., „ . „ „ olivine. 

 (8) Augite-andesites. 



(4) Hypersthene-andesites. 



(5) Hornblende-andesites. 



(6) Augitic trachytes. 



(1) Porphyritic olivine-basalts with very little porphyritic felspar 

 appear to be very common in the south-east of the island. One 

 specimen comes from the summit (F. 289) and one from the foot 

 (F. 287) of the Karu Mahimba Range, and three others from or 

 near a river which drains the southern spurs of that range (F. 2S4, 

 292, and 293). The}' are dark-grey rocks weathering brown, and 

 they show on the fractured surface fresh porphyritic crystals of green 

 olivine and black augite, but no felspar. Under the microscope the 

 augites are seen to be often aggregated into groups ; the individual 

 crystals are sometimes zoned, and they contain fair-sized patches of 

 magnetite. They are slightly pleochroic, in colours of pale yellow 



