HORN EXPEDITION — GENEKAL GEOLOGY. 35 



only ;i week or two, whik' tin- di.st.incc to be trjivcfsed during tluit tiiiu; aiiiouiited 

 to many liundicd miles. Tlie ideological visits of others have been e([ual!y brief, 

 and undertaken under similar unfavouraljle circumstances. Thus no detailed 

 stutly of the rocks was possilde ; all that could be done was to gain a general idea 

 of the whole, and to make, as far as possible, a typical collection of the rocks. 



The occuirence of granite or gneiss in the iMcDonnell Range was made known 

 first by Waterhouse (1) and iStuait (2), and subsetjucntly recorded l)y other 

 travellers. 



Mr. J. J. East (viii., p. 51) makes the following statement : — " It is a reason- 

 al)le presum[)tioii that the beds througln)ut" (this region, /.<., from Lake Eyre to 

 Eserard Plain) " belong to one gi-eat series." As Cretaceous fossils had been found 

 as far north as ilount Daniel, he conckuU's that the rocks of the whole region all 

 lielong to that system. Jle thus includes in the Cretaceous system strata that we 

 now know to contain fossils of < )rdovician (Lower Silurian) age, and a series of 

 rocks underlying these uiiconformaljly, and now termed Pre-Cambrian. Such an 

 hypothesis would have been at any time a most improbable one, and at the present 

 time its acceptance is of course out of the question. " But should their age," 

 continues ^Ir. East (refei'ring to the rocks of the McJJonnell Ranges), "be 

 eonsidtued ^Vrcha-an solely on the ground of their high degree of mctamorphism'?" 

 This author attributes the metamorphism of the rocks of the IMcDonnell Ranges to 

 the presence of " diorite " intrusions. This theory cannot connnend itself to 

 anyone who has ol)served the enormous area occupied by these rocks, and their 

 high degree of metamorphism on the one hand, and the comparatively small size, 

 and in j)hices almcist entire absence, of such "diorite" intrusions on the other. 



This region clearly furnishes an almost typical example fif regional meta- 

 m(_)rpliism, in which great changes, lx»th physical and chemical, have been produced 

 in the rocks l)y extensive earth-movements. 



Mr. IL Y. L. Brown (ix.) sj)eak-s of the "granite and metamor})hic country," 

 and describes the occurrence of garnets and beryl in these rocks. In the sketch- 

 section and map accompanj'ing that report, these rocks are called " Primary 

 Rocks (Azoic)." 



The same author (x., |). 1) describes the rocks of the .McDonnell ]{anges as 

 "Metamorphic and Plutonic Primary Rocks;" and mentions as occurring there 

 "micaceous and hornblendic gneiss, micaceous, liornblen<lic siliceous, and aigillace- 

 ous schists and slates; syenite, garnetiferous granite, micaceous granite; epidocite ; 

 dolomite and crystalline limestone, with erupti\e dykes of iliorite, pegmatilr antl 



