589 



THE ALKALINE PETROGRAPHICAL PROVINCE OF 

 EASTERN AUSTRALIA. 



By H. I. Jensen, D.Sc., late Linnean Macleay Fellow of the 

 Society in Geology. 



In several papers already published* I have discussed the 

 characteristics of the rocks of a number of alkaline areas in Aus- 

 tralia. The evidence given in these papers shows that each of 

 the areas constitutes an alkaline province. In the following 

 notes I propose to summarise the features which the alkaline 

 rocks of all these areas have in common, with the view of showing 

 that the whole of Eastern Australia may be looked upon as 

 having constituted an alkaline province in the early Tertiary 

 period. 



In addition to rocks with a very high percentage of alkali, I 

 include under the heading of alkaline rocks any intermediate and 

 basic rocks in which the composition of the magma has been 

 such as to allow minerals like nepheline, leucite, sodalite, segirite, 

 and allied minerals to crystallise out. Such rocks are looked 

 upon as the more basic differentiation-products of an alkaline 

 magma. 



The principle that rocks of a given region may be genetically 

 related, as formulated by Judd, has already been accepted by 

 most modern petrologists. It has been applied by Pirsson to the 

 rocks of Central Montana,! and with great success by Washington 

 in his recent work on "The Roman Comagmatic Region. "| 



* These Proceedings, 1905, 1906, 1907. 

 t Pirsson, L. V., "The Petrological Province of Central Montana." 

 American Journal of Science, Vol.xx. July, 1905. 



Z Carnegie Institution, 1906. 

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