part 2] or southern eyre peninsula. 81 



As to the dark basic bands which everywhere are seen inter- 

 calated in the acid gneisses, those which are now essentially 

 amphibolites or hornblende-schists are the most numerous. 



I have already referred (in another place) to the occurrence o£ 

 undoubted sediments as rift-blocks derived from the Hutchison 

 Series. The best example of this type is the band of diopside-rock 

 which occurs in the garnet-gneisses of Fishery Bay. This band, 

 oriented with its longer axis parallel to the prevailing gneissic 

 foliation, is identical with the diopside-rocks developed by silicifi- 

 cation of dolomites of the Hutchison Series 3 miles away to the 

 north-east. It has been invaded by f el spathic solutions from the 

 granite, and is clearl}^ an inclusion in the gneiss. 



The amphibolites are dark rocks occurring as well-defined bands 

 in the gneiss, and developed with their longer axes parallel to the 

 foliation in the gneiss. Large masses of quite irregular shape are, 

 however, not uncommon, and, as seen surrounded on all sides by 

 acid gneisses, are convincing evidence that they are of anterior 

 origin . 



In those long and narrow bands, a foliation is often developed, 

 and the amphibolites then pass into hornblende-schists. The 

 foliation is always parallel to the longer axes of these bands, and 

 to the gneissic foliation, except where the band has been broken 

 up by the invading magma and separated into fragments by the 

 maormatie movement. 



IV. The Relationships op the Amphibolites to the 

 Associated Gneisses. 



All the available evidence goes to show that the amphibolites 

 developed in the gneisses — with certain exceptions to be mentioned 

 later — are of anterior origin to the gneisses. The evidence on 

 which this inference is based will now be described. 



The amphibolite-bands range in size from a few inches to many 

 feet in length and breadth. Predominantly, the larger masses are 

 lenticular, or have a length much greater than their breadth, 

 although masses can be met with of quite varied shape. 



As noted above, the elongate character of the bands is such 

 that the longer axes of these are coincident with the foliation of 

 the acid gneisses, and the few exceptions are indicative of a 

 disruption of a band accompanied by separation of the constituent 

 parts. 



In many cases the gneissic foliation has flowed around the bands, 

 being deflected from its prevailing direction at the extremities of 

 the ribbon-like bands, and in other cases, the thermal effect of the 

 enclosing gneiss has rendered the mass sufliciently plastic to conform 

 to the intricate flow-movements in the gneiss itself. Beautiful 

 examples of this structure can be seen on the wave-swept platforms 

 on the coast of the hundred of Lincoln, and it is perhaps best ex- 

 emplified on the eastern shores of the Point Boston promontory 



