412 Transactions. — Geology. 



epoch. This same unequal elevation would also account for the 

 narrow gorge, already mentioned, by which the Waimakariri 

 enters the Canterbury Plains, and which, according to Dr. von 

 Haast, has been entirely cut since the glacier epoch.* If this 

 hypothesis be correct, it follows that the inland sea in which the 

 Waipara, Oamaru, and Pareora rocks were deposited, must have 

 entered the Trelissick Valley from the Waimakariri by Craigie- 

 burn ; the Broken Eiver gorge not having been cut until long 

 afterwards ; and as all these rock systems bear marks of an 

 epoch of subaerial denudation following that of their depo- 

 sition, it follows that the sea entered by this channel at three 

 different times, each time followed by an epoch of upheaval. 



[Addendum.] 



Christchurch, 30th September, 1886. 

 Me. J. D. Enys has informed me that, since my visit to 

 Castle Hill Station, he has discovered a dyke nearly at the top 

 of Gorge Hill — between Broken Eiver and the Porter — which he 

 believes to be a continuation of dyke d. This furnishes abso- 

 lute proof that one of the dykes, at any rate, is younger than 

 the Waipara System ; and probably, therefore, all are younger. 



F. W. H. 



Akt. Lni. — On the so-called Gabbro of Dun Mountain. 



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



[Read before the Philosophical Institute of Canterbury, 4th November, 1886.] 



This is a very coarsely-crystalline rock composed of two minerals 

 only. One is a foliated greenish-brown mineral, like bronzite 

 or diallage, in irregular crystalline masses. The other is an 

 opaque-white or greenish-white felspar, like saussurite. The 

 specimen was given to me by Sir J. von Haast, and I do not 

 know its field relations further than that it comes from the Dun 

 Mountain, near Nelson. Its specific gravity is 3-15. 



The foliated mineral. — Under the lens the principal cleavage 

 planes are seen to be finely striated ; this striation being due to 

 the development of a second plane of cleavage, less perfect than 

 the first, and crossing it at an angle of about 67°. In thin sec- 

 tions, showing both cleavages, the mineral gives brilliant polariza- 

 tion colours, and always extinguishes parallel to the fine 

 striations and oblique to the principal cleavage. This shows 



* " Geology of Canterbury and Westland," p. 213. 



