HORN EXPKDITIOX — ECONOMIC GEOLOCY. 79 



lamina' of wliioli are imieli liciit and opaijuf^, o\'o\\ in tliin ))l,it('s. Tlio lar^ost piece 

 of jNIuscovite mica obtained from tliis claim was, as T was infuiined, nearly six feet 

 in lengtli. Tlie mica was cut into rectangular plates varyini;- in .size by lialf inches, 

 from a few inches up to a foot or more in length, the cutter making the most of 

 the mica, wdiile no attempt was made to cut it into sizes to suit tiie market. 

 When cut it is packed at the mine and conveyed by camel teams to Oodiiadatta, a 

 distance of more than si.\ hundred nules. 



During our \isit only the mica from the surface, which i.«, as stated above, 

 stained brownish-])lack or reddish-brown l>y peroxide of iron or manganese, was 

 being cut and despatched, as there was said to be a good demand for that class of 

 mica for electrical purposes, tlio unstained \aricties being of course too costly to be 

 applied to such a use. 



On the opposite slope of this spur, and a few hundred feet below its summit, 

 there is situated a mica claim, the ownership of which w.is in dispute. 'J'he 

 granite at this claim strikes in an K.S.l'l and ^\^N.^\ , direction, and has an 

 undeilay of about 4.'")'' to th(^ S.S.AN'. A tunned from eight to ten feet in height 

 has l)een driven into the hill along the course of th(i dyke for a distance of thiity 

 feet. The mineralogical composition of this granite is much the same as that of 

 the Oolgarna grainte, with the exception that in the former no l)iotite was observed. 



The muscovite nnc.a, though comiiarativeiy free from oxide of iron stains, was 

 marked with light green sjjots, which would detract somewhat fi'om its \alue. The 

 best of the mica occurs near the south wall, and usually one or more crystal faces 

 are developed. The largest sheet obtained from this dyke measured, when uncut, 

 two feet long, two feet wide, and eighteen inches tliiclc ; and, wlien cut, i ighteen 

 inches in all dimensions. 



Hix nules west of the Oolgai'na claim, and two nules east of Mount Mabclle, 

 another gi'anite dyke is situated, which was being worked by Mv. Luce's l>arty. 

 The nnca was obtained for the most part from shallow open cuttings. A shaft, 

 h()W(!\er, has been sunk on the dyke to a depth of twenty-seven fi^et, at the bottom 

 of which the dyke was found to ha\e naiiowed down from iivc feet, its widlh at 

 the surface to three feet. No mica of any v.ilue was obtaine<l from tlie shaft, 

 wliich was jnit down with the intention of dii\ing eastwards along tiie trend of the 

 dyke, to test its mica contents below the point where it appears widest at the 

 surface. Jn the case of this dyke, too, the largest mica plates were obtained in 

 close proximity to tlu; walls. TIk^ mineralogical composition is identical with tliat 

 of the gr.anite dylvcs described abo\"e. Further west good nnca has been olitained 



