HuTTON. — On the Nelson Boulders. 365 



are therefore probably younger than Devonian. When the 

 boundaries between the eruptive and the surrounding sedi- 

 mentary rocks have been carefully examined, and when the 

 relation of the limestones in Caswell Sound and other places 

 with the diorites has been clearly made out, it will then 

 perhaps be possible to assign them to their proper place with 

 some degree of certainty. And it may be found that the 

 eruptive diorites of Milford Sound are connected with the 

 greenstone-tuffs of the Eoute Burn and Greenstone River, 

 west of Lake Wakatipu, which form the type of the Te Anau 

 series of Sir James Hector. 



Art. XXX. — Note on the Boulders in the Port Hills, Nelson. 

 By Captain F. W. Hutton, F.G.S. 



[Read before the Philosophical Institute of Canterbury^ 4th November, 



1891.] 



A GOOD many years ago I pointed out that the Arrow rock, 

 at the entrance of Nelson Harbour, was composed of a con- 

 glomerate of large boulders, and that boulders of the same 

 nature were also found in the sandstones forming the northern 

 part of the Port Hills.''' These boulders are rounded, go up 

 to 3ft. or more in diameter, and are composed of a granitoid 

 rock which I took to be syenite. Last July, when in Nelson, 

 I collected a fragment of one of these boulders for micro- 

 scopical examination, and find that it is a biotite diorite. 

 There is a small quantity of quartz, but it is quite subordinate 

 to the feldspars, which are chiefly plagioclase, which has suf- 

 fered but little decomposition. The ferro-magnesian con- 

 stituents are biotite and brown hornblende, the former being 

 the more abundant. There is also a little magnetite. 



From this description it will be seen that these boulders 

 differ materially from the syenite of the boulder-bank, in 

 which the orthoclase is more abundant than the plagioclase, 

 and the hornblende much more abundant that the biotite. f I 

 do not know any rock in the district from which these boul- 

 ders could have come, but probably it will be found near 

 Motueka or Separation Point. 



* " Reports of Geological Explorations," 1873-74, p. 49. 

 t Proc. Royal Soc. of N.S. Wales, 1889, p. 124. 



