FEATURES OF TRAP EXTRUSIONS IN NEW JERSEY 315 



pressure which would greatly raise their boiling point. Rather must 

 we suppose that the principal mineralizing effects were due to waters 

 having a temperature but little above 100° C. 



Further evidence of a relatively unobstructed and rapid circulation 

 of water is supplied in the fact that frequently the transparent crystals 

 lining the vugs show inclusions of dark sediment, or again the crust 

 of perfectly formed crystals is covered with a deposit of the same 

 sedimentary material. 



The minerals produced are largely due to the action of these hot 

 waters upon the glassy crusts of rapidly chilled trap. The muds them- 

 selves show practically no alteration except hardening, and the elements 

 of the minerals are those of the igneous rock, with water added. In 

 fact the zeolites seem to be the direct result of the addition of water 

 of crystallization to the albite and anorthite mixtures of the feld- 

 spars and result from a crystallization of previously existing silicate 

 material by a slight modification of its composition. The presence 

 of datolite and apophyllite — compounds carrying boron and fluorine — ■ 

 indicates that the elimination of magmatic vapors from the igneous 

 material was still in progress during the process of formation of the 

 secondary minerals. Such emanations may have been powerful agents 

 in conveying to the channels of circulation material derived from 

 the magma, and in the rearrangement of the various elements 

 present. 



All stages of transition in the alteration of the trap and the forma- 

 tion of minerals from it are common. Frequently we find a breccia 

 with angular fragments of trap as nuclei and crystalhne minerals 

 for a filling. The most perfect crystals, however, form linings to 

 the cavities between the bowlders. I believe there is evidence of a 

 definite sequence in the formation of the minerals but there are diffi- 

 culties in determining it in many cases. Apparently, however, it is 

 as follows : First, a dark green, chloritic mineral, followed by prehnite, 

 datolite, and pectolite; then the zeolites, analcite, laumontite, cha- 

 bazite, natrohte, heulandite and stilbite; ending with apophyllite 

 and thaumasite. Quartz and calcite are very common but seem to 

 have been deposited at several stages and cannot be assigned a definite 

 position in the series. The only metallic minerals observed are chal- 

 copyrite and hematite. Small grains of these, sometimes well crys- 



