REPORTS OF RESEARCH COMiMlTTEES. 321 



higher, averaging 2,900 to 3,000 feet. The area is rough in places, 

 as on the eastern sloipee of the Herberton plateau and in the 

 Tinarco Hills, but there are considerable areas of plain country 

 representing late Tertiary basalt flows. 



The sudden steep fall of the coastal range to the east, and the 

 occurrence of what seem to be Devonian roci?;s on the coastal plain, 

 point to the presence of a big fault immediately east of the Tinarco 

 Hills. 



(e) The Iivinchdnli-Einufoid Area. — This rich mineral district 

 is situated west of the Herberton district, and extends west as far 

 as the Mt. Garnet railway and north tO' the Chillagoe railway. 

 Irvinebank is in the centre. The area consists mainly of rocks of 

 the Herbertonian series (supposed on recent evidence to be Or- 

 dovician). 



The district is very rugged and mountainous, and in most places 

 exceeds 2,500 feet in elevation. 



The rocks most frequently met with are greywackes and chlorite 

 schists, with some slates, quartzites and phyllites, all intruded ex- 

 tensively by porphyries of the Featherbed type and by later 

 granites with their dyke retinue. 



The presence of intmsions of Featherbed porphyries in the Her- 

 bertonian series and their absence in the Hcdgkinson series, the 

 arkose-like- nature of the Herbertonian greywackes and the hard 

 quartzitic nature of the Hodgkinson greywackes, and the presence 

 of chlorite rocks in the Herberton series with the absence of this 

 rock-type in the Hodgkinson series, are striking points of difference 

 between the two series. The rocks of the Hodgkinson series are 

 thus regarded as Devonian and those of the Herberton series as 

 pre-Silurian, probably Ordovician, being intruded by the Feather- 

 bed porphyries which are regarded as of Silurian age. 



(/) The Fcafhcrhcd Rduyt. — This district is very mountainO'Us 

 and rugged. The rocks are of the same types as those of the 

 Irvinebank area, but the porphyries predominate to such an extent 

 that the district is very much more barren than its neighbour to 

 the south. The elevation ranges from 1,500 feet to 2,500 feet. 



(9) The Hn(hj]xiiis<)ii-Ma;/f()Hn Jielt. — This area, commencing 

 north of the Mareeba Dimbula granite mass near the old Minnie 

 Moxham gold mine, consists largely of veiy rugged and very dry 

 country. There are few springs and no permanent waters, except 

 the perennial Mitchell River. 



Slates, steeply inclined or on end, and hard felspathic grey- 

 wackes, which have frequently the appearance of miarclitic 

 trachyte and syenite, are the most plentiful rocks. They weather 

 into rounded hillocks and steep ridges covered with a pebbly 

 rubble which is very severe on horses' feet, giving very bad travel- 

 ling. Roads in this type of country wash out badly in the wet 

 season. 



