532 THE DISTRIBUTION, ETC., OF ALKALINE ROCKS, 



their absorption would take place without producing such an 

 alkaline mixture. 



The chloromelanite and glaucophane-albite schists of the middle 

 and upper zones may often have been produced by the very slow 

 elevation of a deep zone chloromelanite whereby the latter is 

 gradually transmuted to the meso- and epi- types. 



Alkaline gneisses (alkali-felspar-gneiss), glaucophane schists 

 and many other metamorphic rocks have also affinities with the 

 foyaitic magma. 



Now the question arises whether it is not most likely that 

 these alkaline schists are always altered igneous rocks, altered 

 foyaitic lavas and sills. This query has already been partly 

 answered, and we may further object to such an origin on the 

 ground that the upper and middle zone equivalents of jade are 

 unknown. If jade had been derived by metamorphosis of alkaline 

 igneous rocks its epi- and m<°so-varieties should be even more 

 plentiful than the kata-v a,v\Qty. 



It might also be asked if the great abundance of alkaline lavas 

 iu the Tertiary (Eocene particularly) and their comparative 

 rarity in older formations may not be due to old alkaline lavas 

 and intrusives having undergone chemical alterations leading to 

 loss in alkali and gain in lime and other constituents. We have 

 no evidence whatever of any such change taking place. Those 

 undoubted Palaeozoic intrusives such as the alkaline rocks of the 

 Kiama Jamberoo series in New South Wales show no evidence 

 of any such change. The silicates present in alkaline igneous 

 rocks are much the same as those of deepseated schists and are 

 therefore such as would resist metamorphosis unless imbedded 

 for an extremely long time in the upper zone and the top part of 

 the middle zone, and we have no metamorphic rocks in those 

 zones strictly corresponding to the nepheline-syenite magma. 



As far as I am aware, the foyaitic rocks which have long been 

 supposed to be of Palaeozoic age, as in the United States, Brazil 

 and Norway, and which lie surrounded by the schistose rocks of 

 the upper and middle zones, have never shown any passage, or 

 indication of alteration, into chloromelanite, glaucophane-albite 



