380 Transaction*. 



disturbance. All these dykes are white in the hand-specimen, except where 

 they are stained by oxide of iron, which has been derived from the scanty 

 amount of ferro.-magnesian mineral originally present in them, and they are 

 no doubt connected genetically with those occurring in the later basalts, 

 and are not in any way related to the rhyolites in which they are included. 



Bo\ind the shores at the head of the harbour the dykes exhibit extreme 

 irregularity in orientation. On the western shore of Governor's Bav thev 

 strike S.E.-N.W., but on the point running north from Allandale they not 

 only exhibit the same direction, but others have a more easterly trend, while 

 others again, especially towards the end of the peninsula, lie almost N.-S. ; 

 even here, however, large dykes have a S.E.-N.W. orientation. On the 

 east side of this peninsula a large dyke runs parallel with the shore- — -that is, 

 N.-S. — but it is cut by another running E.N.E.-W.S.W. On following the 

 shore to the south their direction averages about S.E.-N.W., but there are 

 several large ones with a N.-S. direction, with a few running E.-W. In the 

 rhyolite quarry on the beach a large dyke strikes S. 15° W. 



In Charteris Bay there is the same variation in orientation. On the 

 road near the wharf the dykes strike generally N.W.-S.E.. but close to the 

 wharf a dyke runs N.E.-S.W. On the southern shore of the bay their 

 direction is various, but chiefly in the sector N.W.-N.E. and S.E.-S.W. 

 There are isolated occurrences outside even these wide limits ; for example, 

 a dvke exposed on the road over the hill to Teddington has a strike 

 E. 25°S.-W. 25° N. 



On Potts Peninsula there is also marked irregularity in direction. At 

 its extremity, opposite Quail Island, they strike N.E.-S.W.. N.-S., and also 

 N.W.-S.E.. with an occasional one E.-W. On the west side of the pen- 

 insula the majority strike E.-W., but numerous others intersect them at 

 all angles, so that they do not appear to radiate from any common centre. 



In the Gebbie's Pass locality the only dykes, apart from the rhyolites, 

 that I have been able to locate are of basalt, with one possible exception 

 in McQueen's Valley. These are oriented in the direction of Quail Island — 

 that is. in the normal direction of those on the outskirts of the volcanic 

 cone. In this sector it is evident that the tough and resistant greywackes 

 and slates proved too strong for the more viscid trachytes, although the 

 liquid basalts were able to penetrate them freely. 



A specially interesting occurrence is that of the tridymite trachyte on 

 the Lyttelton-Sumner Boad, described by Marshall.* The inclination of 

 the mass at an angle of 40° to the vertical, plastered, as it were, against the 

 inner side of the crater, certainly encourages his opinion that it was a flow 

 and not a dyke, but an opportunity of more complete examination afforded 

 by a clearing of the ground has confirmed me in the opinion that it is 

 intrusive in origin. Its lower surface has a dyke contact and not that of 

 a flow, and. further, it is oriented in the proper direction for dykes in that 

 locality. It is cut by two other dykes, both trachytic in character, although 

 one, a hornblende trachyte, is more distinctly basic than the average of this 

 class. Another interesting trachyte dyke occurs at Governor's Bay, where 

 it forms the sea-cliff for several chains, and owing to the action of the 

 weather has developed a most remarkable spheroidal weathering. "f Close 

 alongside this is a glassy trachyte dyke of distinctly alkaline character and 

 with a texture analogous to that of pitch stone. 



*P. Marshall, Tridymite Trachyte of Lyttelton, Trans. X.Z. Inst., vol. 26, 1894, 

 pp. 368-87. 



t J. vox Haast, l"C. fit., p. 335. 



