bv w. n. benson^ \v. s. dun, and w. s. browne. 307 



Tektiarv Igneous Rocks. 

 A tew masses of rock may be referred to this epoch. More than three miles 

 to the south-south-east of Currabubula railway station, in the centre of portion 178, 

 there is an oval patch of basalt, the major and minor axes of which are forty and 

 twenty feet respectively: this is probably a pipe. A second and smaller patch 

 occurs a mile and a half east of t'urrabubula on the lane between portions 31t) 

 and 68. The rocks comprising these are indistinguishable in hand specimen from 

 the normal Tertiary basalt of this State. Mr. Browne considers there is con- 

 siderable similarity between the Tertiary teschenitie dolerites found in the 

 vicinity, e.g., at Goonoo Goonoo (23, p. 703) and near Muriiirundi and the tes- 

 chenitie dolerite occurring south of C'urrabubula township. This similarity is 

 not, however, suflicient to determine that the latter is (jf Tertiary age. 



Recent Alluvium. 

 No features of the Tertiary alluvium call for special comment, except the 

 widespread character of the alluvial fans where gullies open out on to the areas 

 of WeiTie basalt. The distribution of ochreous felsitic detritus on the black 

 soil of the plains at the north side of the Warragimdi hills shows how much 

 alluviation of piedmont plains may be produced, not by definite streams, but 

 merely by the creeping of the soil mantle down the slopes of the hills directly 

 leading to the plains. An extensive alluvial fan has formed at the mouth of 

 Browne's Creek, the result of a land slide whicli occuiTed a few years ago. 



Tectonics. 

 The general structure of the district is simple. As shown in Text-figures 1 

 and 2, it is a syncline, the region mapped in detail forming the eastern limb. 

 This consists of a long secjuence of sediments of Carboniferous age with a total 

 thickness of about fourteen thousand feet, and covered by lava flows of unknown 

 thickness. The whole dips to the west-south-west at an angle varying between 

 28° and 45°. but usually about 37° in the northern portion, but less steeply near 

 Werris Creek. Complexity is brought in by the faults, of which there are two 

 series. The dip-faults are very obvious and numerous and often have a very con- 

 siderable tlirow. Of these the most important is that first made apparent by the 

 discovery of the glncial beds of Browne's Creek and at Proctor's liomestead, which 

 though formerly continuous, have been displaced about half a mile. Approximate 

 determinations show that the downthrow on the southern side of the fault at 

 Currabubula must be about twenty-seven hundred feet. But, where (presum- 

 ably) the same fault crosses the main zone of pyroxene andesite, the downthrow 

 is on the northern side and is only a hundred feet. If we consider this fault to 

 have therefore had a pivotal movement, the present westerly inclination of the 

 beds on tlie soutli side of the fault should be about ten degrees greater than it is 

 on the north, but instead there is no noticeable difference of dip. The same 

 absence of evi<lence of pivotal movement wliere it might be expected arises in 

 other eases as shown below. Parallel to this fault are several other features, 

 the long dyke of hornblende andesite in the north-western portion of the area 

 majaped, the large laccolite of keratophyre west of Currabubula. a narrow zone 

 of crushing which crosses Currabubula ( "reek just below its junction with Rocky 

 Creek, the lower course of the valley of Rocky Creek itself, and the dyke of 

 keratophyre that extends from the "elbow" in this creek, past Proctor's home- 

 stead towards the Gap south of Cobla — these all combine to show that a broad 

 belt of fracturing traverses the Peel Range at this place, into which were injected 



