101 



Several pieces of blue ground, showing cavities from whicli 

 large diamonds have been taken are exhibited. Near the surface 

 the blue gronnd passes into a red soil. 



There is no doubt that these pipes have been drilled through 

 the Earth's Crust by an explosive force acting from within, and 

 they may, therefore, be reasonably expected to continue to a 

 •depth greater than that at which mining would become possible. 

 The blue ground is a breccia composed of a heterogeneous 

 mixture of irregular fragments of various rocks which have been 

 projected upwards from unknown depths. The diamonds have 

 not been formed where they are now found, but have accom- 

 panied the other material in its upward journey. The breccia 

 cannot, therefore, be regarded as the true home of the diamond ; 

 but important evidence, obtained very recently, points to an 

 igneous rock consisting largely of olivine, garnet, and augite as 

 the original source (see |)age IG). 



Some of the minerals associated W'ith the diamonds in the 

 blue ground, eg., bronzite, mica, garnet, calcite, pyrite, gypsum, 

 and natrolite, are exhibited. 



JVest Australia. — A diamond-bearing cement from NuUagine. 



Specimens of spinel, iopaz, emerald, lapis lazuli, garnet, zircon, G-einstones. 

 turquoise, and crocidolite will be found here, but call for little 

 comment. 



Eor leryl, see page 151'. 



2104, Grippsland (Victoria), 9085, Wanganilla (Queensland), Turquoise, 

 and 8525, Arizona, show the mineral as it generally occurs in 

 veins traversing slate. 



This beautiful and well-know^n substance from South Africa Crocidolite. 

 is an asbestos-like mineral that has been saturated with silica 

 .and practically converted into quartz, while stiR retaining its 

 ■ original structure. 



• Specimens from Queensland, Mexico, and Hungary. The Opal, 

 i^ueensland opal generally occurs in veins and masses in iron- 

 •stone. On the wall near the show-case are pictures of the 

 Queensland opal-field. 



