HORN EXPEDITION — GENERAL GEOLOfiY. 47 



Tt is nnfoitunate tliat Mr. Bn>wii ^ivps no .•vocouiit of the o\i(lencos of the 

 uiK'Oiifona.ibility between this scries of I'ocks and liis upper system, wliidi contains 

 fossils determined hy Rlr. Etheridge to l)e Lower Silurian. 



In the following year Mr. Brown (xi\'., p. 7), again classifies the quartzites, 

 dolomite, limestone, sandstone, and slate, which overlie the Pie-Camhrian rocks 

 unconformahly, as Cambrian. He includes in his Cambrian series the rocks 

 occuri-ing between IMount .Sonder and the noi-thern l)oundai'y of the alhuial plain 

 of the Finke, north of the Lutheran Mission Station. There is also on p. 1 1 

 a geological sketch-section showing the relations of the rocks of Mr. Brown's 

 Cambrian system to those above and Ijelow. 



Two sets of observations made; by us pi-ove fatal to ^Fr. Brown's establishment 

 of a Caml)rian System in Central Australia. The lii-st is the presence of fossils of 

 Ordovician age occurring in a dense grey quartzite and in a reddish argillaceous 

 limestone {vide Section McDonnell Range to Levi Range), abnost identical with 

 that found on the noith side of George Gill and Levi Ranges, and recognised to be 

 Oidovician l)y Mr. Brosvn. The quai'tz-grits also associated with limestone at 

 Deep Well, and both limestones and associated gritty sandstones at Chandler's 

 Range contain ( )idovician fossils. The second is the discovery of water-worn 

 fragments of the red Ordovician limestone containing characteristic fossils in the 

 uppermost portion of the mnnense bed of conglomerate and conglomeratic sand- 

 stone, which overlie the quartzites and limestones of Ordovician age {vide Section 

 McDonnell Range to Levi Range), and which form the n(jrthei-n boundaiy of the 

 Missionary Plain, north of the Lutheran Mission Station. The red argillaceous 

 limestone, mentioned above, was found outcropping on the northern side of Horn 

 Valley, which is a longitudinal valley of great length separating two ipiartzite 

 ridges. The actual locality where this fossiliferous limestone was observed is 

 situated ten miles west of the Finke Gorge. The limestone, charged with Ortliis 

 leviensis, was observed to be dipping to the north at a vej-y steep angle, and to be 

 overlain by quartzite. Tt was in tliis quartzite, at a point a few hundred yards 

 south of the northern end of the Finke Gorge, that Endoceras and other Ordovician 

 fossils wei'e also found. Thus \\\ the very centre of Mi\ Brown's so-called 

 Camljrian System, and in I'ocks forming an important part of it, Ordovician fossils 

 have been found. 



The second piece of evidence determines, without a doubt, the age of the 

 conglomerate, also included in Brown's Cambi-ian System, to be not Caml)rian but 

 Post-Ordovician. In view of tlie evidence just mentioned there can be no d<)ul)t 

 that we are pei'fectly justiticd in c(jnsidcring the strata (excepting tlie Post- 



