AVARRE^J. — ALKALI-GRANITES AND PORPHYRIES. 301 



the igneous rocks of the Christiania region where no chemical assimila- 

 tion in place has taken place in the opinion of the workers in that field. 

 The relativel}' thick cover of porphyry, representing as it does the 

 chilled upper portion of the invading mass, which covered a great 

 part of the batholith, is itself another strong evidence that there was 

 not enough original heat, or that the solidification took place so near the 

 surface that the magmatic heat was too rapidly dissipated, even to 

 keep the temperature sufficiently high for a sufficiently long interval 

 to permit of the assumption of a plutonic texture throughout. No 

 differentiation to amount to anything appears to have occurred in 

 either the fine-granite nor the granite-porphyry, excepting in the thin 

 zone of porpliyry found for a short distance along the aporhyolite 

 contact on Pine Hill and at the slate-granite contacts in the Pine Tree 

 Brook area. It is only along the deeper contact levels such as repre- 

 sented the two areas just mentioned, or in the granite directly under 

 its own porphyry cover, where the magma remained hot and per- 

 mitted differentiation to take place, that we find evidences of differ- 

 entiation. Furthermore, complementary dike phenomena, either in 

 the granite or in the adjoining country rocks, are wholly wanting and 

 this is thought to be further evidence that extensive differentiation did 

 not take place. It is believed that such as did occur can now be seen 

 in large part, at least, in the batholith as it stands today. If these 

 deductions are correct the production of the magma by the actual 

 melting of the sediments as proposed and set forth at length by Pro- 

 fessor Crosby in his report on the region, is out of the question. 



That the magma took the place of large volumes of pre-existing 

 rock is certain, and that it did so without appreciably effecting the 

 chemical composition of the magma appears almost equally certain. 

 To accomplish this only two methods of intrusion appear possible to 

 the writer. The first, is that the magma actually pushed up a great 

 block of rock (bysmalithic) thus bringing it up to its present level, 

 which was so near the surface that the magma became chilled so 

 that little differentiation could take place and the heavy mantle of 

 porphyry was developed as a chilled cover. It is certain that the 

 alkaline rocks haA'c suffered some differential movement and that 

 they have been tilted up, relatively at the north. These movements 

 took place along great major fault lines and it is perhaps possible 

 that these may represent lines of weakness along the original lateral 

 contacts of a bysmalithic intrusion. This hypothesis would do away 

 wnth many grave difficulties but there is no proof whatever. The 

 other possible method of intrusion which oft'ers an explanation of the 



