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Transactions . 



if this is the case, a considerable amount of intersection is to be expected, 

 and the district is evidently a favourable one for determining the sequence 

 of intrusions. As to their absolute age, nothing may be certainly stated ; 

 until the boulders in the Cretaceous conglomerates are examined and shown 

 to be similar, it is unsafe to affirm that the dykes are pre-Cretaceous. The 

 petrographical character of the Cretaceous volcanics in the Awatere and 

 Clarence Valleys is as yet unknown, and it seems possible that the coarser 

 rocks that form dykes in Tapuaenuka are intrusions from the same magma 

 that poured out the lavas and the dense dykes intersecting them. In this 

 connection it must be remembered that considerable differential elevation 

 has taken place since Cretaceous times, and that in all probabiUty there 

 was then a continuous sea from the Clarence to the Awatere Valley, over 

 the present site of Mount Tapuaenuka. 



DESCRIPTION OF THE SPECIMENS. 



Minerals. 



As the nature of the minerals is similar in many of the specimens, it will 

 be convenient to notice them first. 



The olivine is a clear variety, with an axial angle approaching 90°. It 

 is penetrated by the usual cracks, along which opaque iron-ores have segre- 

 gated, and shows in addition a fairly Avell-developed schiiler structure, due 



Ohv 



Augite 



Uralite 



Biotite 



Fig. 2. — Olivine - biotite - dolerite crossed by a shear-zone 

 along which uralite has developed from the 

 augite. Magnified 5 diameters. 



to the enclosure of arborescent crystallites of opaque material along vertical 

 planes of the crystals. The commonest alteration is into a tangled mass 

 of talc scales, with occasional prisms of tremolite. This may be termed 



