184: ANNALS NEW YORK ACADEMY, OF SCIENCES 



nations, appear to have ceased by degrees, and the circulating solutions be- 

 came, therefore, principally aqueous solutions which, at relatively low tem- 

 perature, strove to effect among the earlier formed vein materials the re- 

 combinations possible under these changed conditions. The products of min- 

 eral deposition in cavities still open (or produced by destructive work), as 

 well as the products of pseudomorphosis of the earlier formed vein minerals, 

 must, therefore, now become different ; observation shows that almost exclu- 

 sively waterbearing silicates — zeolites — were thereby formed. Just as little 

 as we could draw a sharp boundary between the first and second phases, can 

 we perceive the second and third phases of vein formation to be sharply dif- 

 ferentiated from each other. Indeed, the formation of sulphurbearing ores 

 continued after the beginning of zeolite formation. ... 



That the zeolites have been formed at relatively low (although not ordinary) 

 temperature has been determined with certainty through the researches of Dau- 

 bree, Lemberg, de Schulten and others; apparently the successive changes of 

 temperature with constant decrease thereof has influenced the formation of 

 zeolites in this manner, that certain zeolites can form preferably within a 

 somewhat higher, others within a somewhat lower range of temperature. It 

 appears that in that way most simply can the sequence of the zeolites be ex- 

 plained, which everywhere is in the main nearly constant in the veins of the 

 border-zone. 



The sequence for the deposition of zeolites in open vugs is as a rule the 

 following : 



Analcite, 



Eudidymite, Thomsonite, 



Stilbite, 



Apophyllite. 



Of all the zeolites formed in open vugs, analcite is the oldest and also the 

 most widespread in our veins. . . . 



The analcite is often formed in greatest extent at the expense of the elieo- 

 lite; in part, however, other soda-rich silicates, especially sodalite and albite. 

 have also given rise to the formation of analcite, as will shortly be men- 

 tioned below. Where it has been formed from elfeolite, so much substance 

 appears to have been removed simultaneously in part with its appearance that 

 apparently new open druses were thereby formed, in which besides the anal- 

 cite other minerals also could later be deposited. In part, however, the anal- 

 cite has been deposited in older, preexisting vugs, for it rests often on crystals 

 of leucophane and fluorspar, for example, of the second phase of vein-forma- 

 tion. . . . 



The next zeolite in the sequence is eudidymite, which is only known from 

 one vein upon the island of Ober-Ar6. It rests here upon analcite and is 

 Itself covered with natrolite. . . . 



The normal sequence of zeolites in the vugs of our veins shows natrolite 

 after analcite. . . . 



Apparently simultaneously or nearly simultaneously with the formation of 

 natrolite, that of thomsonite began. 



In a single specimen belonging to the Imperial Museum from an unknown 

 occurrence of our veins, fine blades of stilbite rest upon thomsonite needles as 



