688 GREAT SERPENTINE BELT OP NEW SOUTH WALES, iti., 



gradual increase in density. The following table shows the con 

 dition and density of a number of specimens so chosen that the 

 proportion between pyroxene and felspar should be, as far as 

 possible, equal in each, to exemplify truly the change in rock- 

 density. 



Table showing the increase in the density of the gabbro with 

 increasing mktamorphism. 



Rock. 



NT. 



M.B. 



N.T. 



N.T. 

 M.B. 



, 118 



, 181 



,417 



,477 

 , 17 



Nature. 



N.T.,486 



M.B. 

 M.B. 



43 

 36 



M.B.,51 



Eucrite-gabbro, almost quite fresh . 



Felspar from the same (anorthite) ... 



Chrome-diopside 



Rock much more felspathic than N.T. ,118, entirely 

 changed, with formation of saussurite, a little 

 prehnite and scattered crystals of clinozoisite... 



Rock with less pyroxene than N.T. , 118, and this 

 changed to serpentine; the felspar is saussurite 

 with commencement of formation of garnet 



Gabbro rich in pyroxene, with saussuritised felspar 

 and prehnite... 



Very felspathic gabbro entirely saussuritised, with 

 further changes to prehnite, affecting nearly 

 half 



Rock in which the felspar is almost entirely 

 changed to grossularite, which is passing in 

 turn into prehnite ; but the pyroxene is un- 

 altered 



Rock almost entirely garnet, with a minor amount 

 of prehnite ... 



Garnet-rock, with a very little serpentine 



Prehnite 

 Grossularite 



2 8 



3 55 



Highly crushed gabbro, composed of tremolite, 

 prehnite, and albite 



(7a). The post-peridotite dolerites differ in microscopical char- 

 acters from the earlier dolerites, They have been most studied 

 between the Paling Yard and Crow Mountain, and as yet their 

 equivalents have not been discovered in the Nundle district. 

 They vary considerably in character. Some are intimately 

 associated with the gabbros and peridotites, and have suffered 

 the same alterations to grossularite- and prehnite-bearing types 



