1(V2 HORN EXPEDITION — SUMMARY. 



descendants of tlioso wliiili occupied the area when under nioi-e tavoui'alile climatic 

 conditions tlian now exist, it was })Ossi))lo for plants to spfeacl across 1)0th from the 

 west (Autochtlionian), and from tlie east — especially the north-east (Euionotian). 

 This llora derived pai'tly from the west and partly from the east spi'ead across as 

 the land gradually rose after tJie deposition of the U]>per Cretaceous Ijeds, and 

 whilst, over a wide region of the centiv, the Desei't Sandstone formation was 

 lieing deposited in lacustrine areas. Later on, in Pliocene times, the hygrometric 

 conditions still allowed of an intei'-coinniunication lietwcen the east and west across 

 the centre, but in Post-riiocene times, with the gradual desiccation, the original 

 llora was slowly extinguished, its repiesentat:i\es lingeiing only in fasoured spots. 

 (2) The second element^ consists of a series of more hardy species from the oi-iental 

 region, which gradually spread southwards, until lina,lly the remnants of the 

 original llora. suivi\ed only in (he shady gorges and escarpments of the mountain 

 ivinccs. 



GEOLOGY. 



Tn the reports by Messrs. Tate and Watt the various geological f(M'mations of 

 the ar(>a, traversed are described under the following iieads — Pre-Cainbrian, 

 Oidovician, Post-Ordo^ ician Conglomerate, Upper Cretaceous, Desert Sandstone 

 (.Supra-Cretaceous), Tertiary. 



( 1 ) Pre- Civ/ibriaii. 



These comprise the series clas.sed as Pre-Siluiian by Mr. Chewings and 

 as Archean ])y Mr. IL Y. L. P>rown. Travelling northwards along the oveiland 

 track "a sudden and striking change is ob.sei\ .able in the litliological character 

 of the rocks at the point where those of Pre-Caml)rian age succeed the 

 Lower Silurian, four or five miles south of Alice Spi'ings Telegr.aph Station. 

 Leaving quartzites and limestones we iind ouiselves among rocks of a highly meta- 

 niorphic character, such as gneisses and schists of various kinds." To the north 

 the.se rocks extend to the Burt Plains forming an irregular series of rough, Ijroken 

 hills. East and west, where the junction line l)Ctween the Pre-Canil)rian and 

 Lower Silui'ian rocks can be seen, the latter, resting unconfornial)ly on the former, 

 form a prominent ridge with a steep northern escarpment. In the McDonnell 

 Ilanges alone the rocks now described by Messrs. Tate and W;itt as Pre-Caud)rian 

 are estimated to occupy an area of at least 10,000 square miles, and the "region 

 clearly furnishes an almost typic;il example of I'cgional metamorphism in which 

 great changes, both physical .and chemical, h;i\-e been pi'oduced in the rock's l)y 



