WARREN. — ALKALI-GRANITES AND PORPHYRIES. 299 



that of the pegmatite pipes which have been analyzed and shown to 

 consist essentially of such molecules as Xa2Fe2Si40i2,.(R"iR'2) Fe2Si40i2, 

 where R" equals chiefly Fe" and R', soda, but with small amounts 

 of fluorine and hydroxyl water. Doubtless the riebeckite of the coarse- 

 granite is in large part closely similar, but it appears to pass easily 

 into an alkali-iron hornblende closely allied to the catoforites. The 

 aegirite of the pegmatite pipes consists of the almost pure aegirite 

 molecule Na2Fe2Si40i2 and much of the aegirite of the granite is doubt- 

 less of the same pure variety, but in the earlier formed pyroxene noted, 

 though for the most part rich in aegirite compound, other molecules 

 enter, chiefly one rich in calcium and iron. This molecule appears 

 also as important in the early pyroxene of the rhomben- and granite- 

 porphyry. Again in the granite and granite-porphyry we have 

 aenigmatite or some closely allied species appearing. All this illus- 

 trates well the great complexity of the relationships existing between 

 these soda-iron rich minerals. There are doubtless a number of solid- 

 solution relationships, complicated by polymorphism, concerned in 

 their growth. The formation of one or the other is doubtless effected 

 by the presence of mineralizers, principally fluorine, by differences of 

 pressure and rate of cooling, but of all these things we have at pres- 

 ent such wholly inadequate information that speculation regarding 

 the thermo-chemical relations of these minerals seems too uncertain 

 to be worth venturing further with at present, and such conclusions 

 as those arrived at by Murgoci ^^ regarding the formation of riebeckite 

 and aegirite, interesting and suggestive though they are, must be held 

 open to much question. ^^ 



The intrusion of the Batholith. — The facts developed by the present 

 investigation are obviously too meagre so far as their bearing on the 

 general question of igneous intrusion is concerned to warrant a lengthy 

 discussion of this problem. As bearing on the problem of the intru- 

 sion of this particular mass of rock they are believed to be instructive 

 and fairly complete, and it is hoped that a brief discussion of this 

 particular problem may add a little of value to the more general one. 



There is, the writer believes, convincing evidence ^* that before the 



52 American Journal of Sciences, 20, No. 116, (Aug., 1905). 



53 See also in this connection Warren & Palache, op. cit., p. 144. 



54 The evidence is not direct, so far as the pre-Cambrian sediments and 

 granites are concerned, since the Quincy rocks are nowhere found in igneous 

 contact with these rocks. Both to the north in Essex Co., and to the south 

 in northern Rhode Island, there are intrusions of alkaline granites so similar 

 to the Quincy that there can be no doubt that they are of the same age. These 

 are known to cut an older, biotite granite. Their intrusion was preceded, 



