110 



vesicular lavas,* and between the pebbles o£ the conglomerates. 

 Occasionally boulders of copper have resulted from the com- 

 plete replacement of portions of the rock. It seems most pro- 

 bable that the copper has been derived from some of the mineral 

 constituents of the igneous rocks. The exhibit from this field is 

 very complete, and well exemplifies the mode of arrangement 

 followed in the Museum. The series commences with a few 

 picked specimens of native copper, followed by the crushing 

 ores, samples of coarse screenings and concentrates in different 

 degrees of fineness, the country-rocks in different positions and 

 mines, and associated minerals. 



At the head of the case will be found descriptive labels, maps, 

 and plans. 



In this case (84) may be noticed — 7439, crystallised native 

 copper, and 5205, native copper welded to native silver. 



2059j a quartz-porphyry pebble from one of the conglomerate 

 beds, which are sometimes largely made up of igneous material. 



2060, the contact of melaphyre with conglomerate. The 

 amygdaloidal character of the melaphyre will be noticed. 



Larger specimens will be found in upright case 103, which 

 show^ the structure of the country well, viz. : — 



3402, conglomerate with large pebbles of porphyry showing 

 native copper and junction with melaphyre. 

 3412 ; somcAvhat similar to the above. 



3407, Tamarack Mine ; a good specimen of copper-bearing 

 conglomerate with pebbles of porphyry. 



3398, Tamarack Mine ; a large pebble almost entirely replaced 

 by native copper. 



This replacement of a porphj-ry pebble by native copper is a telling- 

 instance of the powerful action of mineralising solutions under the 

 conditions prevailing in the Earth's Crust. 

 Arizona. ^^ ^\^, the third in importance of the American copper 



fields, the ores are in the main oxidised. A special feature is 

 the beautiful crystals of azurite (blue carbonate of copper) 



* For similar occurrences in Australia, see page 65. 



