356 Morris MorrlM: 



magma becomes pi-ogressively more aeid. In tlir Damleiioiigs, lio\v- 

 ever. the order of exti-usioii was progiessively less aeid. This order 

 is also exemplified in the Buohan district (12), where the L. 

 Devonian igneous activity opened with ([uai'tz porphyries and 

 rhvolites, and closed in some cases with andesites. 



e. NOMENCI.ATUKK OF THP: I(;NKOrS KoCKS. 



There can be no doubt that a true classification ought to be genea- 

 logical, and it should also provide a nomenclature that would make 

 it possible to give a generic name to all the meml)ers of any family 

 of rocks, which have been produced by modification during descent 

 from the same parent magma. 



If we accept Hatch's classification, as it stands, then, in the case 

 before us. the plutonic rock of tlie Belgrave i-ailway line is too poor 

 in SiO^ [63.85 per cent. (Richards), and 64.41 per cent. (Plant)] 

 to be called a granodiorite. 



Further, taking the five volcanic series, the Upper series, hitherto 

 called the " Hypersthene Dacite," would l)e the only one of the five 

 which w-as not a dacite. No analysis has appeared, where its SiO^ 

 rises to 66 per cent. But, as all tliese series belong to one family, 

 and that of obvious dacitic character, Hatch's boundary line should 

 be elastic enough to enable us to give them all the same family 

 name. Series e is therefore called the " Upper Dacite Series." 



The first two series, containing nearly 7 per cent, of alkalis, and 

 nearly 70 per cent, of SiOo. form a paii- of alkali dacites. As the 

 ground mass of the first is full of orthoclase. while that of the later 

 is microcrystalline, I proposed at first to name them respectively, 

 " Orthoclase Alkali Dacite Series," and " Micvoi-rystalline Alkaline 

 Dacite Series." For the sake of simplicity, however. 1 have called 

 them " The Lower," and " The Upper Toscanite Series," in con- 

 formity with the existing classification, though there is nothing in 

 those names to indicate any consaTiguineity of these with the re- 

 maining three series. 



In view of these two toscanites (alkali dacites), in which no quartz 

 is to be seen except in the ground mass, wliere it is not greatly de- 

 veloped, it seems inadvisable to phue too mmh reliance on Hatch's 

 rule that dacites are minei-alogically distinguished from andesites 

 by the presence of quartz. 



The last three volcanic series have been named for simplicity, 

 " Lower," " Middle," and " Upper Dacite Series " resi)ect ively. 



