Hill. — On Distribution of Pumice. 295 



lava-flows, or that it is only produced on the surface of such 

 flows. There is sufficient evidence in the volcanic district of 

 this island to show that such is not the case. 



Pumice is usually of a dull grey, varying to a pale straw 

 colour, although there are many places, both within and without 

 the volcanic zone, where the pumice varies from a deep red to a 

 pale salmou colour. The varieties, however, both in colour and 

 composition are legion ; in fact, a scale might be made of varie- 

 ties of pumice, passing gradually from a beautiful white flour- 

 like pumice, through coarse sand grit and boulder pumice, to a 

 variety much resembling a trachyte, and thence to a kind of 

 cross between a pumice and an obsidian. The numerous speci- 

 mens on the table will fully illustrate this statement. Obsidian 

 froth would perhaps best describe the pumice pebbles, such as 

 are brought down from the pumice fields on the Taupo Plain by 

 the Ngaruroro, Mohaka, and other rivers in time of flood, the 

 composition of pumice and obsidian being almost identical. 

 Although pumice appears to be so very light, its specific gravity 

 is from two to two and a half times the weight of water. In 

 other words, a cubic foot of pumice would weigh from 2,000 to 

 2,500 ounces. The beautiful specimen of obsidian which was 

 found lately at the mouth of the Turanganui Eiver, and which 

 I have brought down for inspection by members, will give some 

 idea as to the actual specific gravity of an apparently light sub- 

 stance like pumice. 



As far as my own observations extend, no volcanic product 

 is more widely diffused over the North Island of New Zealand 

 than pumice and trachyte-pumice, which is a pumice containing 

 small felspar crystals within its mass. The surface of the 

 country within a radius of thirty miles or more of Lake Taupo 

 is composed of nothing but pumice, underlaid for the most part 

 by trachytic-lava rocks. Were I dealing with the character of 

 the rocks found in the volcanic zone, as I hope to do at some 

 future time, I should endeavour to account for the origin of the 

 vast pumice deposits of that district ; but my purpose in the 

 present paper is to show how far the country to the eastward of 

 the volcanic zone, and extending from the great central mountain 

 chain forming the Euahine, Kaimanawa, and Te Whiti Eanges 

 to the sea, on the one hand, and from Tologa Bay (latitude 

 38° 20' S.j to Cape Turnagain (latitude 40° 30' S.), on the 

 other, has been affected directly and indirectly by volcanic 

 products in the shape of pumice and other ejectamenta. My 

 second object is to trace the geological distribution of this im- 

 portant product. 



The district named above may be said to contain an area 

 of 5,000 square miles, and, as far as I am aware, there are 

 only three places in the whole of this area where traces of 

 igneous rocks are to be met with. These places are (1st) at 



