West Tamar District, Tasmania. 159 



the same direction as those of the adjoining silurian rocks ; 

 below which, and in the valley, the rock loses all traces of 

 stratification, and occurs in a great variety of forms of very 

 variable composition. It is full of veins of chrysotile, an 

 analysis of which in Mr. Newbery's laboratory, by Mr. 

 Frederick Dunn, gave — 



Silica 43-55 



Magnesia 



Protoxide of iron 



Lime 



Alumina 



Water (combined) 



3804 

 6-41 



traces. 



11-67 



99-67 



Occasionally grains of chromite and magnetite are thickly 

 distributed in layers. Magnetite also occurs in thin veins, 

 and unconnected, striated, or longitudinally grooved slabs, 

 with asbestus lying in the external grooves. The decom- 

 posed rock often contains veins and nodules of %vad (hydrous 

 oxide of manganese). Singularly enough this mineral is never 

 seen in the undecomposed rock. From a shaft on the top of 

 Mount Vulcan, the rock contains thin veins of a mamillated, 

 apple-green, soft, waxy -looking, translucent mineral, which, 

 by a blowpipe determination by Mr. Morley, proved to be 

 genthite, or silicate of nickel, a somewhat analogous occur- 

 rence to the nickel ores of New Caledonia. All the rain 

 channels off the serpentine hills contain minute, glittering, 

 black octahedrons of chromite and magnetite. A small 

 feldspathic or euritic granite dyke traverses the centre of 

 the serpentine in the usual strike of the country. On the 

 east side of the serpentine hills there is a variable amount of 

 local attraction from north towards west. 



The carboniferous rocks, consisting of nearly horizontal 

 conglomerates, sandstones, limestones, &c, occupy generally 

 all the low levels round the western arms of the Tamar. 

 They rest against the flanks of the silurian ranges, pass 

 under the greenstone, and reappear again on the eastern 

 side of the river on the eastern flanks of the Tippagory 

 Ranges, where the eastern edge of the basin rests against 

 silurian rocks in the same way as its western edge does. 

 This formation includes some valuable beds of limestone, 

 exceedingly rich in fossils. A totally unconnected occur- 

 rence of these rocks is on the high divide separating the head 



N 



