Wild. — Geology of the Bluff. 



319 



Point. A study of the rocks in this locality, together with those of 

 Tewaewae Point, reveals the nature of the metamorphism, though the gap 

 in the series occupied by the mouth of the harbour cannot be bridged in 

 a manner absolutely satisfactory. 



The origin of Bluff Harbour and Awarua Bay, as well as Waitur>a 

 and other lagoons along the south coast between Bluff Hill and Fortrose, 

 requires some explanation. 



The sand and shingle driven by the prevailing current through 

 Foveaux Strait came to rest at the lee side of Bluff Hill. Thence, after 

 the manner commonly described, a sandbank extended outwards in a 

 direction slightly north of east. At length it reached the headland of 

 Waipapa and Slope Points, which attains a height of 800 ft., or slightly 



Tewaewae Pt- 

 Plutonic— Norite. 

 Plutonic^- Basic secretion. 

 Hypabasal— Porphyry. 

 Metamorphic—Hornhlpnde schist 

 Amphibolite. 



A I- 



10 15 20 CHS. 



1 



=1 



Starling P l 



Fig. 2. — Geological Map of the Bluff. 



more, some twenty miles to the east. Thus a considerable area of water 

 was cut off and enclosed by the sandspit. As the sandbank received 

 further additions it increased in height and mass most rapidly at its 

 eastern end, where its onward progress was stopped by the headland 

 already named. Finally, at its lowest end — that is, immediately 

 adjacent to Bluff Hill — the waters broke over the barricade, and restored 

 communication with the ocean. The channel was made across the 

 intruded rocks, possibly along a groove commenced by the ancient rivers, 

 and long since filled in with sand and alluvium. This channel, once 

 begun, was rapidly deepened by the inrush and outflow of the tide, 

 which in the middle of the channel travels at the present time at the 

 rate of eight knots an hour, such is the size of the basin to be filled. 



Subsequently this large lagoon was subdivided by lateral sandspits, 

 and Waituna Lagoon was separated from Awarua Bay, and a separate 

 outlet was formed. 



