70 GEOLOGICAL REMARKS. 



for the immediate purposes of navigation in those 

 parts. 



The fact of the existence of several active volcanoes 

 on islands immediately adjacent to the north coast 

 of New Guinea (first made known by Dampier)^ and 

 the circumstance of volcanic bands traversing" the 

 leng'th of many of the great islands of the Malayan 

 Archipelag-O; and others as far to the southward as New 

 Caledonia and New Zealand^ rendered it extremely 

 probable that we should have found indisputable 

 signs of comparatively recent volcanic action in the 

 south-east part of New Guinea. We saw no vol- 

 canoes^ however^ and the great central mountain 

 chain appeared to me to be probably granitic. The 

 large Brumer Island is composed of igneous rocks 

 as formerly mentioned j and at Dufaure Island I 

 obtained from some canoes which came off to us a 

 few smooth water-worn pieces of hornblendic por- 

 phyry. Some specimens of obsidian^ or volcanic glass^ 

 were also procured from the natives at the latter 

 place^ where sharp-edged fragnnents are used for 

 shaving with; one variety is blacky another of a 

 light reddish-brown, Avith dark streaks. Mount 

 Astrolabe is apparently of trap formation, as I have 

 already stated. Some conical hills scattered along* 

 the coast may possibly be of volcanic origin, especially 

 one of that form rising to the height of 645 feet 

 from the low land behind Redscar Head. It is in 

 this neighbourhood also that we find the upraised 

 calcareous rocks of modern date exhibited by the 



