44 Canadian Record of Science. 



district on which there is an almost continuous succession 

 of granites from Peuig to away beyond Bohringen, and 

 which is as much as 1 J km. broad, should be as deep as it 

 is long. Let us assume, however, only half this depth, 

 17J km." etc., etc. That granite can be formed at such a 

 depth is indeed possible ; there are certainly, however, no 

 grounds for such an assertion. On the other hand, it may 

 be demonstrated from the Christiania district with the 

 greatest certainty, that the granitites and other post-Silu- 

 rian plutonic rocks occurring here, were formed at a much 

 less depth below the then existing surface. The laccolitie 

 mass of granite at Drammen, for instance, is covered by 

 Silurian strata of Etage 8 ; it is here, therefore, absolutely 

 certain that, at the time of its formation, it can have been 

 covered at the very most by a superimposed mass ! of about 

 2,000 ft., or about 600 m. At other places in the Christiania 

 district, the depths at which the plutonic rocks (augite 

 syenite at Kodal, in Kamnas, etc.,) have solidified were only 

 a few hundred feet ; this is absolutely certain, as here they 

 continue upwards into the porphyry covering. Also at 

 Langesundfjord, where the augite syenites and nepheline 

 syenites come into contact with the the augite porphyries 

 and rhombic porphyries, the depth at which the solidifica- 

 tion of the nepheline syenite occurred can have been only 

 a few hundred feet. At Heivand, between Skien and Slem- 

 dal, the nordmarkite mass is similarly overspread with a 

 cover of rhombic porphyry; hence the depth at which the 

 nordmarkite mass solidified can have been at most only a 

 few hundred feet. These observations are numerous and 

 indisputable, and they demonstrate unequivocally that a 

 depth of even a few hundred metres was sufficient to pro- 

 duce by solidification true eugranitic plutonic rocks from 

 that part of the magma which did not reach the surface. 

 Whether also at the depths postulated by Lehmann, 1*7,500 

 or 35,000 m., granitic magmas solidify to plutonic rocks or 



1 Namely, a few hundred feet of Etage 8, then Devonian sandstone 1,000 to 

 2,000 feet, then a few hundred feet of augite porphyry and rhombic porphyry. 

 The only uncertainty is with regard to the thickness of the rhombic porphyry 

 covering, but thousands of feet it certainly cannot have been. 



