98 



of this formation, still striking N.S., continue as far as Annean 

 Station where they carry the Annean Reef, the first gold reef dis- 

 covered on the Murchison. 



DESCRIPTIVE GEOLOGY. 



Fundamental Rock Structure. — Exclusive of the recent and 

 superficial deposits, the general geological configuration of the 

 country may be best described by assuming as foundation two 

 massive masses of granite, forming slightly undulating high 

 plateaux, which are bordered, one of them to the E., and one to 

 the N. and E., by low hills composed of crystalline metamorpliic 

 rocks. One of these masses, the smaller, extends from the Yil- 

 garn Hills to the east as far as the Depot Hill of Hunt (near Camp 

 77), from which point eastwards the granite is overlain again by 

 metamorphic rocks, which is probably the case also to the north 

 and south. The other granite mass, the larger, extends from 

 Yilgarn northwards as far as Townsend Station, and is flanked 

 on the east by a belt of schistose rocks. How far this belt ex- 

 tends towards the east is not yet known, but if it should not be 

 continuous T should think that slaty rocks prevail in this region 

 just as the granites do to west of our route, where the slate 

 formation, according to Mr. H. P. Woodward, Government 

 Geologist in W.A., in his report on this country, and also accord- 

 ing to Rev. W. B. Clarke, in his •' Sedimentary Formations of 

 N.S.W.," only occurs in patches. 



Cainozoic Rocks. — The following recent formations to bo found 

 in this part of West Australia are : — 



Sandy Plains. — These are the chief features of this tract of 

 country, and they consist either of a fine loose sand, or, more 

 frecpently, of a hard loamy sand. In the latter case they give 

 rise to splendid vegetation and high timber, whilst that on the 

 first-mentioned kind is in every sense entirely useless. In the 

 Murchison District the sand of these plains is found consolidated 

 to such an extent that it can be used as a building stone. It is 

 three to five feet under the surface where this recent sandstone 

 is found in layers of five to ten feet in thickness, interstratified 

 in places by a semi-opaline sinter, and almost invariably, and 

 chiefly at a shallow depth, it is found to be water-bearing. 



If freshly broken this sandstone is very friable, but hardens 

 (luickly by exposure to the air, a circumstance which points to the 

 presence of a fair amount of calcareous matter besides silica. The 

 sand forming these sand-plains may be taken as the derivative 

 material of the " Desert Sandstone" which still covers vast tracts 

 in the interior. Immense areas also are covered with sand and 

 gravel, consisting of ferruginous sandstone and claystones. They 

 have a widespread occurrence between the Lake Lefroy country 



