166 HORN EXPEDITION — SUMMARY. 



(3) Post-Ordovicia>i Conglomerate. 



Tliis cdiigloiiieiate Hanks tlie southern face of the (juartzite ridge wliich foiius 

 the northern boundary of the Missionary Plains and the southern boundary of the 

 Horn Valley. The lower parts of the conglomerate consist of fragments derived 

 from the Ordovician strata and in this pebbles of red limestone were obtained 

 containing tlie following Ordovician fossils: — Aitiitoceras fatet\ Fn/icana wattii, 

 Oft/iis diiJiotoDialis. The Post-Ordovician age of this conglomerate was thus 

 clearly established. The upper layers were most largely made up of pebbles 

 derivcti from the Pre-Canibrian rocks, and the total thickness of the conglomerate 

 and conglomeratic sandstone was estimated by Mr. Watt, who carefully examined 

 it during a traverse of the ranges, to be not less than 7000 feet. 



(4) Upper Cretaceous. 



The Cretaceous {)lains and table land sUipe gradually from their northern 

 limit somewhere in the neighbourhood of IMount Durrell Station, where they have 

 an elevation of not less than 1000 feet to Lake Eyre in the south wIk^c their 

 surface; is thirty-nine feet below sea level. 



From these stony and loamy plains i-ise table-toppe<l hills capped with Desert 

 Sandstone. 



The table-land formation is recognised as contemporaneous with the Rolling 

 Downs series of Queensland, which has been assigned by Messrs. Etheridge and 

 Jack* to the Lower Cretaceous series but, according to Messrs. Tate and Watt, 

 " the facies of the fauna is more akin to that of the European Ujiper Cretaceous 

 while the palajontological differences between it and the De.sert Sandstone are 

 too slight to justify the application of the terms Lower and Upper tt> them 

 respectively." The Rolling Downs formation and its equivalent series forming 

 the table-lands and plain of the Centi-al area are therefore recognized as Upper 

 Cretaceous. The formation is essentially an argillaceous one and the Oodnadatta 

 bore which reaches a depth of 1571 feet shows a series " varying from clay shale 

 to marly clay intercalated with which are thin argillaceous limestones and some 

 sand beds ; these latter occur at various horizons, and the chief supply of water 

 was obtainetl in the basal sands of the section. Thus the general character of the 

 strata passed through is like that of other bore sections in the Lake Eyre basin."t 

 Above the level plains rise low hills of which Mount Daniel with an elevation 



* Geolog-y of Queensland, etc., p. 3i)0. t Geolo^'V, Part III., p. G2. 



