102 THE VOYAGE OF H.M.S. CHALLENGER. 



to attach to the volcanoes of this archipelago, and the somewhat advanced state 

 of our knowledge concerning the geology of the great islands constituting it, scarcely 

 any precise details were known of the lithological nature of the island and volcano of 

 Camiguin. The specimens collected by the Challenger naturalists make it possible in a 

 certain measure to fill up this blank. 



The study of the products of the volcano of Camiguin is, as will be seen, very 

 closely related to the study of the substratum on which it has been formed, accordingly 

 it will not be useless to give a short sketch of the geological constitution of the 

 archipelago. As we have just said, some recent volcanic rocks of this group have 

 been worked out by various able geologists, but the examination of the rocks of the 

 subsoil and of the sedimentary formation have not been the object of such detailed 

 researches. 



It has nevertheless been established that the greater part of the underlying rocks 

 of the Philippines belongs to the schisto-crystalline series ; on these the sedimentary 

 beds are deposited, and the latter, which are partly to be referred to the eocene period, 

 are in their turn covered over by more recent deposits. There are, besides, to be 

 observed some raised coral reefs, sometimes containing mollusca belonging to a species 

 still living in the Pacific. 



Finally, certain eruptive products, which are, according to von Richtofen, 1 later 

 than the nummulitic limestone, iire overlaid by deposits that must be referred to the 

 present period. Some of the rocks found at Luzon and Zebu contain fossils of an 

 older period. 2 When describing the rocks of Zebu, it will be shown that certain 

 eruptive rocks of that island ought to be referred to the pre-tertiary series. The 

 existence of granite in the archipelago is a fact of very great importance, and must 

 be taken into account in explaining the origin of the material ejected by the volcano 

 of Camiguin. Von Humboldt 3 points to the north of Luzon as containing masses of 

 that rock. In the same region Jagor collected rocks of the granitic type, but he 

 did not see them in situ, his specimens consisting of rounded pebbles. In other parts 

 euphotide, serpentine, diorite, spilites, and epidotiferous rocks have been observed. 

 Crystalline schists, gneiss, mica schists, amphibolites, and chloritic rocks, associated with 

 the older eruptive series, play a more conspicuous part in the geological constitution 

 of the island than do the recent volcanic formations. It is to these ancient schisto- 

 crystalline rocks that certain well-known metalliferous deposits in the Philippines 

 belon.a'. 



4 



1 In Roth, loc. cit., p. 334. 



2 Ibid., p. 333. 



3 See Humboldt, Kosmos, vol. vi. p. 405. 



4 Roth, loc. cit., p. 334. The existence of ancient crystalline rocks in the Philippine Islands is pointed out in 

 several passages in Professor Roth's memoir. R. von Drasche in his geology of Luzon admits that the gneissose rocks, 

 the diabases, and the gabbros form to some extent the framework of the southern part of the island. 



