588 



THE DISTRIBUTION, ETC., OF ALKALINE ROCKS. 



(in fig. 11) given a sketch showing the distribution of land and 

 sea in Palaeozoic times. These maps make it clear that our Aus- 

 tralian alkaline rocks occupy, roughly speaking, a position which 

 has been a coast-line or near a coast-line for many geological 

 periods. This line appears to have been a hinge in all the earth- 

 movements since the Palaeozoic, and alternately the blocks on the 

 one side or the other of it have been slowly uplifted or depressed. 



Fig. 13. — Relation of Line of Outcrop of Alkaline Rocks to 

 Cretaceous Coast-line. 



It has not been heavily sedimented, but it has been greatly 

 faulted, in the Tertiary periods particularly. 



This line is therefore one of the grandest structural features 

 of Australia, and probably contains the key to the solution of 

 many problems in Australian geology. 



The text-figures also show that the trachyte-line follows with 

 more exactness, as far as we can tell, the Triassic and Trias-Jura 

 coast-lines than the Cretaceous coast. 



