295i • H. 8. Summers : 



weir, for some miles down stream the fall of the river is fairly 

 rapid, and there is no apparent cause why the stream should 

 build up its bed over 70ft., and then set to work to carve out a 

 new channel for itself in the granite. 



The absence of typical striated boulders is, of course, a strong 

 argument against the glacial origin of the conglomerates, but 

 this absence may be partially explained by the fact that the bulk 

 of the pebbles are composed of quartzite, granite and porphyry. 

 The first named being extremely hard, may have resisted scratch- 

 ing, and only show polishing, and the decomposition of the sur- 

 face of the igneous rocks would remove all traces of striations, if 

 such had ever been present. 



(D). — Alluviuin. 



The distribution of the alluvium is shown in the accompanying 

 map. In part this is rich river wash, but the lower level mate- 

 rial is compos'ed mainly of resorted material from the conglo- 

 merate with only a small proportion of finer material. 



IV. — Petrogeapht. 

 The igneous rocks of this area may be divided for the time 

 being into granite, granite porph\Ty and quartz porphyrv", the 

 discussion as to their correct nomenclature being reserved until 

 later. Aplitic and pegmatitic veins are associated with the 

 granite. 



(A). — Granite. 



The granites are only found to occur at the lower levels along 

 the valley of the Broken River. The colour of most of the rock 

 ia red, this colour being sieoondary and due to the alteration of 

 the felspars and ferro-magnesian minerals. 



The structure of the rock is peculiar, as it has a porplip'itic 

 appearance, due U> the fact that large blebs of quartz and felspar 

 crystals are set in a gi-anular mixture of quartz and felspar, with 

 here and there a granophyric intergi-owth of quartz and felspar. 

 Cross sections of the large quartz grains show a rough hexagonal 

 outline, and the large felspars show fairly perfect crystal boun- 

 daries. Flakes of white mica with a pearly lustre are present, 

 and biotite showing considerable alteration is moderately abun- 

 dant. 



