112 Transactions. 



south-east of the main peak is a steep rocky peak of about 1,000 ft. ; and 

 to the south-west of the main peak are several smaller peaks, all, however, 

 with gentle slopes. Three-quarters of a mile along the ridge to the north- 

 east of the main peak is a small elevation known as McGregor's Hill. On 

 the south and east the hill slopes down to the shallow waters of Otago 

 Harbour, and at the south-western end to an enclosed bay known as Lake 

 Logan. The gullies on the eastern and southern sides are of slight depth, 

 and are occupied by small streams. 



A valley of considerable breadth and depth runs down to Lake Logan, 

 and is occupied by the Opoho Stream, which rises in a swampy area near 

 the summit of Signal Hill. On the north-west the ridge is bounded by 

 the North-east Valley Stream. This stream always carries a considerable 

 volume of water, and has eroded for itself a deep valley. The sequence of 

 the rocks appears to indicate a great antiquity for this stream-valley. The 

 stream has two branches, one of which rises on Mount Cargill, while the 

 other has worked its head back in an easterly direction, and is cutting down 

 the saddle to the north of McGregor's Hill. The upper part of this branch 

 is still eroding its bed, but the lower part, and also the main stream, have 

 reached base-level, and have filled the floor of the valley with alluvium. 

 The North-east Valley Stream is fed by numerous small tributaries, the 

 middle courses of which are generally through steep-sided gullies. 



Occurrence op the Rocks. 



The rocks of most widespread occurrence within the Signal Hill area are 

 the phonolite of the Logan's Point type, the trachytoid phonolite of the 

 Signal Hill type, and a basalt-flow which I describe as basalt No. 1. The 

 basalt covers the top of Signal Hill, and extends across the upper part of 

 the depression of the North-east Valley. The Logan's Point phonolite 

 extends from near the summit of the hill to Logan's Point, forms a steep 

 peak on the side of Signal Hill overlooking the harbour, and reaches to a 

 point near Burke's. The Signal Hill phonolite has rather a wide occurrence 

 about McGregor's Hill, and is found also in the North-east Valley. 



Besides these there is a distinct variety of nephelinitoid phonolite, 

 occurring probably as an intrusion, on the saddle to the north of McGregor's 

 Hill ; and there are several other basalts. The latter vary in composition 

 from a very basic variety, occurring as a dyke on the Mam North Road, 

 which appears to be the youngest rock described, to a variety approaching 

 andesite, which appears to be the oldest rock exposed. The least basic of 

 the basalts, which I have called No. 5, clearly underlies the Logan's Point 

 phonolite at a point on the Main North Road a quarter of a mile from 

 Normanby. In the valley below this point it is not to be found, being 

 obscured by slips of phonolite from above. Between the phonolite and the 

 underlying basalt in the section exposed there is a stream-deposit, with 

 boulders derived from the basalt, proving an intermediate period of erosion. 



The Logan's Point trachytoid phonolite mass is of great thickness on 

 the southern slope of Signal Hill, being continuous from below sea-level 

 at Logan's Point to an elevation of 1,100 ft. near the summit. Towards 

 the west, however, it thins out, until on the Main North Road there is a 

 thickness of only 50 ft. between basalt No. 5 below and the main basalt- 

 flow (No. 1) above. 



In the valley below, the Logan's Point phonolite gives place to the Signal 

 Hill phonolite, but the junction is obscure. There is difficulty also in 

 tracinif the boundarv between the two rocks on the eastern side. It is^ 



