WoELEY. — On the Nelson Boulder Bank. 223 



said. This ridge of hill, being composed of soft sandstones 

 and clays similar to the rocks in the clifl" and on the beach, 

 has, with the exception of what remains at the cliffs, been 

 washed away. The hard core of this ridge, composed of rock 

 similar to the Arrow Eock remains, however, as an upstand- 

 ing reef, forming the basis of the Boulder Bank. 



Having shown that the existence of a reef under the 

 Boulder Bank is highly probable, the next point for con- 

 sideration is the nature of the rock of which this reef is com- 

 posed. That the reef is similar to the Arrow Eock has already 

 been remarked, but the Arrow Eock is only a fragment of 

 an extensive belt of rock, and probably does not adequately 

 represent the whole. An inspection of the Arrow Eock shows 

 that it is made up partly of solid syenite rock and partly of 

 syenite boulders firmly cemented together into a conglomerate. 

 There is also in the syenite an intrusive sheet of lava. The 

 boulders referred to form a part of the Arrow Eock, but lying 

 around its base there are numbers of loose boulders which at 

 one time doubtless formed part of the solid mass. These 

 boulders are syenite, and quite similar to some of those found 

 on the bank. 



When the Torpedo Corps were improving the entrance to the 

 harbour they blasted away rock made up of syenite boulders, 

 and owing to its stubborn resistance found they could make 

 but very httle impression upon it with their charges of gun- 

 cotton."^ Such, then, is the kind of reef that probably under- 

 lies the Boulder Bank— a boulder stratum, underlain by solid 

 syenite, turned up on its edge by the upheaving force that 

 raised the Port Hills. 



There is no need to go into the origin of this boulder 

 stratum beyond stating that it is probably the result of glacial 

 action. In the cliffs above the Eocks Eoad several boulders 

 of syenite have been unearthed. These stones prove con- 

 clusively that boulders were being carried in that direction 

 while the rocks in which they are imbedded were being laid 

 down as horizontal strata. 



Given such a reef as has been described, then the origin of 

 the Boulder Bank and the formation of Nelson Haven become 

 simple matters, unbeset by any difficulties; and easily under- 

 stood. 



This theory of the Boulder Bank does not preclude the 

 possibility of drift having come from Mackay's Bluff. In all 

 probability — one might almost say certainly — boulders and 

 shingle have drifted from there along the bank. This theory 

 of the underlying reef, however, gives to the Boulder Bank its 

 alignment, and removes some of the difficulties which make it 

 hard to accept the purely drift theory. Some of these diffi- 

 culties will now be mentioned. 



