238 .7. F. KEMP AFTER-EFFECTS OF IGNEOUS INTRUSION 



Even when the recrystallization does not go so far, one may trace in 

 some granites an extraordinarily progressive series, from inclusions of 

 schists, angular and not much changed, through others charged with 

 granitic minerals, on through still others, the mere outlines and ghosts 

 of th^ir former selves, until only a few shreds and basic streaks of biotite 

 remain. The Stony Creek granite of Connecticut, 18 taken from quarries 

 a few miles east of New Haven, is at times very prolific in these phe- 

 nomena. The foundations and lower courses of the buildings of Columbia 

 University display in the cut blocks extremely instructive illustrations. 



As remarked, the xenoliths caught up in granite and related intrusives 

 are often sharp in their outlines and show no absorption of their sub- 

 stance by the inclosing magma. When they were captured the magma 

 was probably cold enough to be near the point of consolidation. Such 

 xenoliths, however, have sometimes produced an effect on the magma 

 analogous to catalyzers, or stimulants of reactions, although not them- 

 selves affected. One may observe strongly pegmatitic developments har- 

 bored, so to speak, in the lee of the inclusions, as if the mineralizers had 

 gathered next them and had brought to pass localized and very coarse 

 ervstallizations. This pegmatitic phase may contain coarse magnetite, 

 tourmaline, and rarer minerals, all characteristic of the work of mill* 

 eralizers. 



Actual Analyses of escaping Gases at volcanic Vents 



kilauea, by day axd shepherd 



I may next raise the question, How much do we know regarding the 

 actual composition of the emissions ? In so far as effusive rocks are trust- 

 worthy representatives of deep-seated intrusives, we may cite the actual 

 analyses of escaping gases. The best and most carefully made determi- 

 nations which have been published as yet are those of Day and Shepherd, 19 

 from the basaltic magmas of Kilauea. "Water, escaping as a gas and 

 caught and condensed as a liquid, was the most abundant emission. It 

 was followed by carbon dioxide, nitrogen, hydrogen, carbon monoxide, 

 and sulphur dioxide. Dissolved in the water, which was condensed in 

 the tubes, were fluorine, sulphur trioxide, chlorine, and in one sample a 

 very little ammonia. There were also the common bases of the igneous 

 rock^ — soda, potash, lime, ferric oxide, alumina, and in one sample a 

 questionable trace of titanium dioxide. No silica is reported, and the 

 authors remark that the bases might have been derived frorg the glass of 

 the conductors and condensers. 



