8 F. L. ^StiUiuell: 



twinning, and one is therefore inclined to call it anorthoclase. It is 

 probable that the chemical composition of the rock is not far different 

 from the Central Red, White and Blue type, where the soda is in excess 

 of the potash, and this assists the determination as anorthoclase. Tlie 

 presence of this anorthoclase (?) base distinguishes the rock from 

 the typical monchiquites. 



Specimen No. 5, Forbets Carshalton Mine. The specimen 

 was obtained from the dump heap without any knowledge of 

 its depth in the mine. Tlie locality is more than one mile 

 north of the Goldfields No. 1 shaft. Like the Goldfields' rock 

 this rock is generally similar to the monchiquites. Olivine is mostly 

 serpentinised, and the augite is present in two generations. Horn- 

 blende and ilmenite are perhaps in smaller proportion than in the 

 typical monchiquite. These minerals are all set in a ground mass of 

 felspar laths. The felspar shows lamellar twinning, and the lamellae 

 give extinction angles up to 35 degrees, which determines it as labra- 

 dorite. This felspar is present in much the same proportion as the 

 isotropic material in the type monchiquite. In addition it appears on 

 the segregation patches similar to the light coloured, acid residual 

 areas in the monchiquite. Clearly this felspar has been the last mineral 

 to crystallise during the consolidation of the magma, and in this 

 respect it is certainly analogous to the isotropic material of the mon- 

 chiquite. 



The felspar of this rock and of the Goldtields No. 1 indicates that 

 they belong to the camptoiiitic variety of lamprophyre. Tbe Forbes 

 Carshalton specimen is more of a true cami)tonite than the Goldtields 

 No. 1 sample, with its alkali felspar. It seems to be very similar to 

 a rock found at Balwyn, which occurred as a small flow. This has been 

 described by Messrs. Chapman and Thiele (10) as a limhurgite. 



The examination suggests that the labradorite and anorthoclase 

 are but further stages in the crystallisatiaon of the monchiquite 

 magma. The distribution of each as a base for the other minerals is 

 very similar, and their relative proportions are much the same. This, 

 combined with the minute amount of felspar in the monchiquite itself, 

 suggests the passage from, the true monchiquite through the Gold- 

 fields No. I. type to the Forbes Carshalton type. The specific gravities 

 of the two last-named are greater than the specific gravity of the 

 Central Red, White and Blue type. This is in accordance with the 

 suggestion Ijecausc the specific gravity of a glass is always less than 

 that of the mineral which would result fi-om it. 



Specimen No. 38. One Tree Hill Mine. (Plate 1., Fig. 2). This speci- 

 men was collected l»y Mr. Whitelaw, and was obtained from a now 

 inaccessible part of tlie One Tree Hill Mine, two miles to the S.S.W. 

 of Bendiy;o. The One Tree Hill anticlinal axis is some distance to the 



