HORN EXPEDITION PHYSICAL fiEOfiRAPIIY. 7 



wliicli it is ;ili)iosfc vortical. At the foot of tills oscaipinont tliero is a talus slope 

 nearly 200 feet liigh, witli an inclination of about 30°. 



(3) Cretaceous Table-topped Hills and Table-lands. 



Although thoro aro no mountains or mountain i-angos woi-thy of tho name 

 within the Cretaceous cUvi.sion, the altitude of the Cretaceous plains near the 

 northern limit of this area is as much as 1000 feet above sea level. These 

 elevated plains slopes gradually towards Lake Eyre from an altitude of 1000 feet 

 above sea level to thirty-nine feet below sea level at Lake Eyre. 



Rising out of these plains art; numei-ous table-topped hills and low tla.t ranges 

 and table-lands, i.solated from one another by denudation. Some of the highest of 

 these rise to an altitude of from 300 to 400 feet above the suri-ounding plains, and 

 thus in the northern part of this Ci-etaceous area to 1200 to 1300 feet abo\e sea 

 level. These isolated masses are separated by " stony " and " loamy " plains and 

 "sandhills." The iiills are usually crowned by a layer a few feet in thickness of 

 an exceedingly hard rock, representing somc^times a sandstone, sometim(^s a grit, 

 and at other times a finer-grained and more argillaceous rock. Between the grains 

 of this rock hydrated silica has been deposited from solution. To the pivsence of 

 this cement is to be atti-ibuted its extreme hardness and often move or less 

 conchoidal fracture. This so-called " desei-t sandstone," or poivellanite, when 

 finer-grained and more argillaceouis, protects the under-lying strata from denuda- 

 tion in a way that may be compared to the protective action of the boulders in the 

 case of the famous earth-pillars of certaiii villages in the Tyrol. 



Chandjers Pillar, for instance, a well-known feature situated ten miles north 

 of the old Idracowra cattle station on the Einkc, nnght. b<' likened to an earth 

 pillar, the indui'ated ferruginous sandstone of its sunnnit taking the place of th(! 

 boulder of the earth-pillai-, and protecting the sandstone of the j)illar from renio\al 

 by denudation. The isolation of Chambers Pillai', for it is surrounded on all sides 

 by red sandhills, is probaljly due to the purely local character of the indurating 

 process, or rather perhaps to the induration having lieen more intense in the 

 locality of the Pillar, than in the once surrounding rock, now eritirely denuded. 

 The Pillar, if we include in this tei'ui the whole structui'e from base to sunnnit, is 

 divisible into two parts — a basal portion oi- pedestal .')00 yai'ds in cii-cumf(>r(>nce at 

 its base and 100 feet high, and a column surmounting it, sixty-seven feet high and 

 eighty yards in circumf(!rence at its l)ase. The whole, witii the exception of the 

 few feet of moic indurated rock on its summit, consist.s of a \cllow and wiiitc; 



