HORN EXPEDITION — GENERAL OEOLOCiY. 49 



Oi-dovii'i;iii Systpin of rocks so strongly devoloped to tlio ucirtli of ]\rouiit Burrell 

 and between this point and the JMoDonnell Ranges, aiul w liicli h.i\(^ now yielded 

 Ordovician fossils in so many localities. 



In this report Mr. Brown distinguishes an ovei'lying series " composed of 

 hrown and wliite sandstone in horizontal and inclined layeis," and called by him 

 Devonian (?) ; hut as this author in a latei' report (xiv., p. 7) relin([uishes this 

 division, it will not be necessiiiy to make any comment. 



In his topographical description of the country lying between the Flinders 

 and McDonnell Ranges, Mi'. East (viii., p. 31) treats the subject under three 

 headings, viz., (1) "The Great Austral Plain," (2) "The Terraces," and (.3) "The 

 Gi-eat Central Plateau." Had Mr. East- divided this ai'ca geologically into three 

 corresponding divisions, the rocks of each belonging to one nf the geological 

 systems, he would have made an approximation to the truth, if he had called 

 the rocks occurring in the area included in his first topographical dixision Cre- 

 taceous, those of the second (Silurian, and those of the third Pre-Cimbrian, he 

 would have given an infinitely superior geological classification than that suggesteil 

 by the following statement (viii., p. .'')1) : — 



"With regard to the geological age of this region" (l)etween Lake Eyre and 

 Everard Plain on the north side of the McDonnell Ranges) "the presence of fossils 

 on the face of the slope up to an altitude of SUO feet" (referring probably to the 

 discovery by himself of Li)i^^ii!a siiliovalis at Mount Daniel) " places us on pretty 

 sure ground and shows the age of deposition to be Mesozoic, and probably Cre- 

 taceous. F.arther up tli(^ slope there must exist doubt until fossils are actually 

 discovered, though it is a reasonable presumption that tiie beds through<iut l)elong 

 to one gi'eat series." 



In criticising this statement it must be bornc^ in mind that it was not until 

 two years after the publication of Mr. East's paper that Lower Silurian fossils 

 were first described from Central Australia. After making due allow;uice, 

 liowevcr, for the aljsence of pala'ontological evidence to the north of Mount 

 Daniel, it is difficult to understand how any geol(jgist, who had travelled over the 

 Cretaceous, Silurian, and Pre-Cambrian rocks, could formulate such a tln'oiy. The 

 rocks of the three .systems under consideration diti'er from (jne another in litho- 

 logical characters and structui'al features as much as it is possible for any three 

 sets of I'ocks to do. Not only so, Init the change in these features is sudden anil 

 well-marked, even though the actu;il junction-line itself be not observed. Tiius 

 the CiM'taceous rocks ha\'e \'ery ch.aracterist ic litliological eli/irai-l ers, an<l dip at 



