HORN EXPEDITION — GENERAL GEOLOGY. 59 



Ohst'i-vations made; furtlirr to the west in the Horn Valley provt^ that red 

 fo.ssiliferoiis limeslone underlies the last mentioned rock. iSoutli of this last {)oint 

 there is a gieat thickness of quartzite dipping at high angles to the north. This 

 is overlain unconforniably l>y a thick bed of conglomerate of Post-Ordovician age. 



The s(;ction in i\[ere(Uiie BluH' presents the following succession of beds in 

 descending order ; the thicknesses are Ijy estimate : — 



Thickness. 



Quartzite ...._. 300 feet. 



Yellow friable sandstone --------- 300 „ 



Dark iirown or purple shales with intercalations in the lower portion 



vi blue, calcareous, arenaceous shales u\> to 7 feet thick - - 100 ,, 



Calcareous shales with many thin liinestone-ljandS; the upper ones with 



Isoarcii, the lower ones with Ortliis levicnsis - - - - 60 „ 



Unseen ------------ ■? 



Quartzite forming the south escarpment of Horn V^alley. 



For general stratigraphical features see Section froui Mereenie Bluff to Belt 

 Range. 



(/) Isolated Portions of Ordoviciau. 



Tiie most southern isolated mass of ()rdovician rocks examined Ijy us, 

 with the possible exception of Ayers Rock and Mount Olga, was a quartzite 

 hill, which Mr. Winnecke named Mount Watt, and which is situated about 

 twenty-four miles west of Engoordina on the FiidvC. This hill, together with 

 a more elongated mass lying to thi3 north of it, which there was no time to 

 e.Kamin(>, is situated well within the area occupied superficially by rocks of 

 Cretaceous age. From its sunnnit the tlat-topped hills, so characteristic of the 

 Cretaceous formation, could be seen on all sides ; while iunuediately surrounding 

 it red sand-hills clothed with Triodia formed the pre\ailing feature, and swept 

 almost up to its base. This hill, which rises to an elevation of 240 feet above the 

 surrounding .sand-hills and 1300 feet above sea level (according to Mr. Winnecke's 

 calculation of the altitude of Camp 11 at the foot of the hill), is composed from 

 base to sunnnit of a hard, dense quartzite, with a talus of the same material sur- 

 rounding its base. The .strike of the quartzite varies from N. 50" E. to N. 60° E., 

 and the dip varies in amount from 7' to 10°. The greater part of the (piartzite is 

 of a grey colour, but there ai'c a few red ferruginous bands, one about six feet and 

 another fourteen feet from the sunnnit, the latter band having a thickness of 

 twenty-live feet. The rock is much fissured, one set of cracks running nearly 

 parallel with the strike. 



8A 



