546 Harry Page Woodward — Geology of Western Australia. 



Geological Features.^ 



In describing the geological features it will be necessary to 

 divide the country into six sections : namely, the North, North-west, 

 West, South-west, South, and Central. 



The North or Kimberley section embraces all the country to the 

 northward of Roebuck Bay and eastward to the northern territory 

 of South Australia. It consists mostly of broken country and is 

 -very interesting geologically, as many good sections of the Palseozoic 

 rocks are exposed in the river gorges. Near the coast the Upper 

 Carboniferous series is largely developed, whilst the Devonian, 

 Silurian, Cambrian, and Archgean rocks are met with further inland. 

 Moreover, associated with these older rocks there occur rich deposits 

 of gold at the heads of the Ord and Fitzroy rivers, whilst to the 

 eastward, on the border of the colony, one of the largest known 

 basaltic lava-flows is met with. 



Along the North-west coast the country is also much broken, but 

 here the crystalline and granitic rocks outcrop directly from the 

 alluvium with occasional bold hills and ridges of trap-rock, and it 

 is amongst these that the gold deposits of Pilbarra are found. 

 Further to the southward there is a table-land composed partly of 

 Dolomite and partly of Basalt, but these formations are of no great 

 thickness as the clay slates are exposed in the Ashburton valley, 

 where some important discoveries of gold have been made. 



The Western section stretches south from North-west Cape to 

 Champion Bay, and consists of low cliffs formed of later Tertiary 

 strata. Inland, in the northern part, a sandy plain extends for some 

 20 or 30 miles, as far as a narrow ridge of Mesozoic hills running 

 north and south, and is followed to the eastward by a belt of 

 Lower Carboniferous rocks which immediately overlie the crystal- 

 line schists. South of the Murchison River, near Northampton and 

 Geraldton, a fine series of Mesozoic rocks is exposed in the broken 

 table-land near the coast. These formations rest unconformably 

 upon the crystalline rocks, with their rich copper and lead-lodes. 



The South-western coast consists of low-lying sand-plains of recent 

 origin, with many salt estuaries, lakes, and swamps, which extend 

 inland for a distance of from 10 to 20 miles. Rising abruptly upon the 

 eastern side of these plains is the Darling Range, composed of crystal- 

 line rocks, which attain a general elevation of about 1000 feet above 

 the sea-level. The surface of this range and the country for about 

 50 miles to the eastward of it, is mostly covered by deposits of 

 indurated nodular ferruginous clay-stones called "ironstone gravel." 

 This deposit is often of considerable thickness, and, particularly 

 upon the high ridges, is often cemented together into blocks of 

 conglomerate called " ironstone." 



In the river flat of the Collie, on the east side of the range, about 

 30 miles from the coast. Coal-measures have lately been discovered, 

 and a fine series of seams has been proved to exist by boring. 

 Nevertheless, no outcrop of this formation is visible at the surface, 



' See a Notice of Geological Map and recent publications on Western Australia, 

 in G-EOL. Mag. September Number, pp. 420-425. 



