274 Transactions. — Geolofjy. 



through which is scattered some ilmenite, and occasionally a 

 chloritic mineral. A second brownish -green augite is also 

 present. This answers very closely to Giimbel's definition of 

 leucophyre, as quoted by Teall,* except that in our rock the 

 augite is in very considerable quantity. 



This, therefore, may be taken as the name of the rock. It 

 differs from dolerite in the subordinate position of the felspar 

 and in the green augite ; it is, in fact, an augite rock with some 

 plagioclase and iron oxide ; sometimes, however, the saussurite 

 appears to be as abundant as the augite. That it is an altered 

 rock is undoubted, and it may perhaps be an altered dolerite. 

 Its grauulitic texture shows that it consolidated during move- 

 ment, and its association with beds of volcanic ash shows that it 

 is an old lava stream, probably of Triassic age. 



Art. XXXVI. — On the Oxford Chalk Deposit, Canterbury, New 



Zealand. 



By Henry Wilson, B.A. 



[Read before the Philosophical Institute of Canterbury, 2nd June, 1887.] 



Plate XV. 



The Ashley County seems peculiarly rich in interesting 

 geological formations, but to none does more interest attach 

 itself than to the small patch of chalk near Oxford. This chalk 

 was reported on as far back as 1881 (vide Geological Reports), 

 by Mr. McKay, of the Geological Department. Mr. McKay's 

 report of the bed is so accurate tbat my description must in 

 part traverse his. There are, however, some interesting par- 

 ticulars with regard to the fossils contained in the chalk that 

 have been passed over in his report, and to these I shall have 

 the pleasure of calling your attention. Besides the question of 

 fossils, there is the interesting question of the distance from 

 land at which a chalk, almost as free from impurities as 

 English chalk, may be formed. 



This chalk, then, is situated in and almost wholly composes 

 one small hill : this bill forming, in one direction, the extremity 

 of the bush-clad bills lying around the base of Mount Oxford. 



As will be seen by a reference to the accompanying diagram 

 (Plate XV.), the bill is skirted on three sides by streams ; while 

 on the fourth there is a valley, so that the chalk hill is, to use 

 a Scotticism, " self-contained." 



* " British Petrography," p. 135 



