498 THE DISTRIBUTION, ETC., OF ALKALINE ROCKS, 



In New England the Cretaceous intrusions and Tertiary lava 

 flows mark a number of periods of instability, which inaugurated 

 renewed elevation of the plateau. 



To the Neopyrogenic period belong in addition all the Tertiary 

 lavas of Eastern Australia, including the alkaline volcanic masses 

 of the Warrumbungles, Nandewars, Mittagong, East Moreton, 

 Mount Flinders, &c, and all the Tertiary rhyolites and basalts 

 of our eastern States. 



Andrews has shown that the New England intrusions have 

 assimilated to a notable extent the invaded rocks, a feature 

 which has been observed in other parts of the world by R. A. 

 Daley, A. E. Barlow, H. N. Winchell, A. P. Coleman, and A. 

 Harker.* 



The extensive researches of E. C. Andrews have established 

 the following facts for a part of New South Wales — 



(1) A period of subsidence of long duration and free from 

 volcanic action preceded a pyrogenic period (in the case of New 

 England, the Mesopyrogenic). 



(2) The commencement of elevation was accompanied by 

 immense igneous intrusions. 



(3) A long period of rest followed elevation. During this 

 period erosion and peneplanation were effected. Then followed 

 subsidence or instability. 



(4) Renewed volcanic activity (in New England, the Neopyro- 

 genic) followed. 



(5) Then came renewed elevation followed by stable conditions 

 and erosion. 



These facts seem to me to afford strong evidence in favour of 

 Mellard Reade's theory of the formation of mountain-masses 

 through rise in isogeotherms in sediments deposited during a 

 period of prolonged subsidence. The isogeotherms rise; folding 

 results; magmas rise from beneath through fractures and are 

 thrust into zones of no strain in the sedimentary anticlines. 



* Andrews, New England Geology, Part iv., Records of the Geol. Survey 

 of N.S.W., Vol. viii., 1907. 



