94 ANNALS NEW YORK ACADEMY OF SCIENCES 



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Natrolite 172 



Apophyllite 173 



Chlorite 174 



Serpentine 174 



Third period of alteration 175 



Calcite 175 



Thaumasite and gypsum 177 



III. Comparison with other deposits and general conclusions 178 



Resume 185 



,%- Introduction 



Certain localities within the area covered by the basaltic ridge which 

 forms the First AVatchimg Mountain in Northern New Jersey have for 

 many years been famous among mineral collectors in the East for the 

 beautiful specimens of zeolitic minerals which they have yielded. Al- 

 though from a purely utilitarian point of view nothing of economic value 

 has been discovered among these minerals or their associates, yet to the 

 mineralogist, the size and perfection of crystal groups and the delicacy of 

 form and coloring which are exhibited render them most attractive and 

 desirable acquisitions. In these respects, the finest specimens found in 

 the New Jersey localities are but little inferior to the similar zeolitic 

 groups brought from the world-famous collecting-grounds at Berufiord in 

 Iceland and the Poonah District in India. 



Beyond the attraction which these minerals offer as objects of beauty 

 or from a mineralogic standpoint, they present to the geologist many 

 problems which add greatly to their interest. From this side, the rela- 

 tions which they bear to the enclosing rock and the cause and manner of 

 their deposition are matters of greater importance. It is easy to recognize 

 from their field associations that the veins and pockets in which they are 

 found have many points of similarity with metalliferous veins, and that a 

 full understanding of the processes involved in the formation of the zeo- 

 lites would be of the greatest value in interpreting certain of the features 

 of the economically important metalliferous deposits. From another 

 point of view, one can recognize in the genesis of the zeolites a phase of 

 manifestation of the processes of hydrothermal metamorphism, which 

 operate in various forms to alter the crystalline cliaracter and the min- 

 eralogic composition of igneous and sedimentary rocks. 



Study of the zeolites by various workers has resulted in considerable 

 literature on the subject. The greater part of what has been written, 

 however, deals purely with the crystallographic or optic properties of the 



