162 THE BUILDING OF EASTERN AUSTRALIA 



felsites, graphic granites, gneiss, augen gneiss, basalt, 

 andesite and gabbro. 



The sedimentary rocks comprise quartziteSj mica 

 schists, andalusite schists, marbles and limestones. 



The western portions of Australia, which are so 

 largely of Pre- Cambrian age, have probably in the main, 

 escaped heavy sedimentation in all subsequent geological 

 periods, for otherwise a heavy coat of later sediments 

 would frequently hide the Pre- Cambrian rocks. Western 

 Australia was, therefore, uplifted at an early period. 

 / It formed part of a Pre- Cambrian landmass which ex- 

 tended in a north-west direction to Arabia and Abys- 

 sinia and south- wards to Antarctica. This great landmass 

 was probably fairly persistent throughout Palaeozoic 

 times, since Africa, India and Australia had a similar 

 flora up to the end of the Palaeozoic, namely the Lepi- 

 dodendron flora of the Carboniferous and the Glossopteris 

 flora of the Per mo- Carboniferous. 



The absence of sediments newer than Pre- Cambrian 

 over large areas of Western Australia, is not the sole 

 evidence for supposing this area to have been essentially 

 a continental mass from that remote geological age to 

 the present. A strip of the west coast of W.A. was sub- 

 jected to several marine transgressions in late Palaeozoic 

 and Mesozoic times, but sedimentation was neither 

 prolonged nor heavy, for practically all deposits later 

 than Pre- Cambrian are almost undisturbed by any 

 compressional forces, their dip seldom exceeding 20°. 

 The sediments of various later geogolical ages are deposited 

 upon highly folded, inclined and contorted rocks, con- 

 sisting of schists, conglomerates, gneisses and igneous 

 rocks of the Pre- Cambrian complex. Even the Cam- 

 brian rocks, such as the Nullagine series of Pilbarra, 

 are little disturbed. The Nullagine, Carboniferous, 

 Permian and Mesozoic rocks, where in juxtaposition, 

 are not easily separable by such criteria as hardness, 

 metamorphism, difference in angle of dip, and so forth, 

 but mainly by the occurrence of unconformities between 

 them. Consequently the transgressions of the ocean 

 in these periods did not interfere with the geological 

 unity or plateau character of Western Australia. 



