BY H. I. JENSEN, D.SC. 175 



by deep water, and not by a sea of coral islands. This 

 implies fast movement such as would be produced by fault- 

 ing. If the movement had been slow the corals would 

 have been able to keep building up at the same pace as the 

 the downward sag, and islands would be scattered through 

 the whole expanse between the reef and the mainland. 



Fig. 13 gives the writer's idea of this block. In it 

 we have a repetition of the processes which build up 

 mountain folds and caused the gradual easterly aggrandise- 

 ment of Gondwana land. 



In North Queensland, in the Tertiary period, a plateau 

 uplift gave rise to a plain extending as far as the present 

 Barrier Reef. This plain was faulted, and the seaward 

 portion sagged downward. During this process, volcanic 

 extravasation took place. The subsiding block is getting 

 heavily sedimented, and its western portions are at the 

 same time having their isogeotherms raised by the intrusion 

 of basic magmas as indicated by the recent basalt flows and 

 hot springs of N.Q. The conditions are, therefore, favour- 

 able to the productions of great fold^ in this block, which 

 in due course will become uplifted and a part of the con- 

 tinent. The down movement of the block will continue 

 until rise of isogeotherms in the sediments is able to over- 

 come the pressure of the sediments. 



It strikes the student of geology that folding move- 

 ments were more intense in the Palaeozoic periods than 

 later in the earth's history. This, if so, would seem to 

 corroborate Kelvin's theory of the origin of the earth, 

 for it would indicate that in the Palaeozoic, the earth's 

 crust was more plastic and the zone of flowage nearer to 

 the surface than at present. 



VULCANICITY AND PETROLOGY. 



The petrology of the sedimentary rocks of each of 

 the great Palaeozoic periods is naturally very similar through- 

 out Eastern Australia. Though similar rocks are not 

 always contemporaneous, and sometimes one series, some- 

 times another, is missing in various parts of the continent, 

 still a general resemblance exists between the sedimentary 

 formations of each period for all parts on the same belt 

 of sedimentation, and this lithological similarity can often 

 be verified by the discovery of fossils. 



