GEOLOGICAL DIVISIONS. 201 



of the above described marine strata is locally varied by the presence 

 of great igneous masses. 



These are seldom true granites, but more frequently syenites and 

 diorites, with a granitic holocrystalline structure of varying degrees 

 of coarseness. The nature of the rock varies greatly from place to 

 place, and nearly all the great masses are traversed by dykes 

 of somewhat more basic composition. These basic dykes, the latest 

 results of the series of phenomena that gave rise to these intrusions, 

 occur in many regions, traversing the sedimentary rocks where the 

 larger intrusions are absent. 



These intrusions have been regarded as contemporaneous with 

 the great volcanic outbursts of the "flysch" 



Age of the intrusions. 



being in fact subterranean manifestations of 

 the same set of phenomena. This is not exactly-- the impression 

 which I gathered from the facts observed in the different regions 

 visited. 



It has been mentioned above, that the volcanic strata extend right 

 through the upper cretaceous and the greater part of the eocene, 

 but that they become more scanty as the section rises. In almost 

 every instance the great intrusions are found to have been injected 

 amongst strata full of nummulites, so that they are certainly newer 

 than a very great proportion of the observed volcanic rocks; still 

 as there are important volcanic agglomerates apparently of middle 

 eocene age at Saindak, it might be said that the intrusions represent 

 the underground products of some of the later eruptions. Even then, 

 there is this more to be considered. The rocks are holocrystalline, 

 often coarse-grained, and present all the characters of plutonic 

 rocks. They cannot have been formed except under a considerable 

 mass of superincumbent strata, and it is therefore in any case 

 necessary to regard them as much younger than the youngest pro- 

 ducts of true eruptions that have been observed, so far as the flysch 

 period is concerned. 



Another line of reasoning which tends to make them appear 

 much younger in age than the flysch eruptions is as follows. There 



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