finds difficulty in applying this distinction. He doubtfully 

 classes as enallogenous gabbros and norites in basaltic tuff 

 and basalt in various parts of France, believing them to be 

 fragments of older formations, on account of their passage 

 into rocks containing garnet, quartz or biotite, and presum- 

 ably of ancient origin. 1 At the same time lie considers 

 certain augite-plagioclase inclusions in basalt at Coirons 

 to be homoeogenous, admitting the uncertainty of the 

 former classification. 2 In later works ; Lacroix developes a 

 subdivision of the homceogenous group into the following 

 divisions:— the allomorphous, fragments of masses already 

 consolidated at depth ; plesiomorphous, segregations formed 

 in the magma which have not had a separate existence as 

 geological units; the polygenous and pneumatogenous 

 divisions do not here concern us. The allomorphous and 

 plesiomorphous inclusions are further subdivided into homo- 

 logous, formed by the mean type of the enclosing magma, 

 and the antilogous formed by basic differentiation or original 

 heterogeneity. 4 



Applying all this to our present problem :— if we were to 

 consider the Dundas inclusions as enallogenous we would 

 require to assume the existence of a batholith of basic and 

 ultrabasic rocks underlying nearly the whole of the eastern 

 portion of New South Wales. So large a batholith of rocks 

 of this basicity is almost without precedent. Further, 

 though underlying a district of very diverse geological 

 character, it never appears at the surface, unless we take 

 as portions of it the Carboniferous (?) norites of Kiandra, 

 described by Mr. E. C. Andrews'' or the gabbro of Adelong 



. i'.KU, pp. is-. 



< groupes d'enclaves des roches eruptives, tfuii. ooc. 



Note.— For this 'summary of Lacroix' views I am indebted to the 

 paper prepared by Mr. J. A. Thomson, on the Inclusions of the Volcanic 



i Boss Archipelago, to appear in the Geological ] 



onnsn Antan.-tn: Expedition, 1007 - 1000. 

 Department of Mines N.S.W., Mineral Resources, No. ] 



