i66 



ALFRED C. LANE 



stony margin (An. 2) in its less silica, more lime and magnesia is not 

 so far on the toboggan slide toward the goal of "wet differenti- 

 ation" — the magma from whence crystallizes pegmatite veins, and 

 not so near to a granite (An. 4) as the glassy center (An. i). We 

 seem thus to have caught two stages in a differentiation which 

 carried on on a large scale would lead to the hornblende granites 

 described by Dresser. 



As to the syntexis upon which Daly lays stress, there is no 

 doubt that the inclusion and absorption of fragments of sandstone, 

 especially if they contained water in the interstices, should promote 

 the formation of micropegmatite, and zones of micropegmatite 

 around such fragments in process of absorption are found in the 

 Medford diabase, as Jaggar and others have seen. Possibly the 

 water is quite as important as the sihca. Very likely much of 

 the red rock of Pigeon Point is of this nature. But the association 

 of micropegmatite with diabases is too widespread for me to agree 

 with Daly^ that most granites are differentiates of syntectics. It 

 is well worth considering how many are, like that described by 

 Dresser, direct differentiates with the help of juvenile juices or 

 mineralizers. 



* Including o . 02 CI. 0.24 PaOs t Including o . 2 PaOs . 



t Bowen in Can. Mining Inst., Vol. XII (igop), p. 523, diabase, including 14 S. 



§ Ibid., granite cutting diabase, including i.oo COj. 



' Op. cit., p. 312, etc. 



