FENNER, THE WATCHVNG BASALT 95 



minerals. It has been found that the optic characteristics present many 

 anomalies, not all of which have found explanation, and that the laws 

 governing the crystallographic forms of the various species are very com- 

 plex, especially as regards twinning. These are matters which are largely 

 of a physical nature and are apart from the scope of the present paper. 

 They will not be considered, except that the results which have been 

 attained will be utilized as offering valuable criteria for determination 

 and discrimination. Efforts have also been made to determine the order 

 of succession of the various associated species from different localities, 

 but, so far as the writer is aware, the resources of microscopic petrography 

 have been little utilized in this direction. 



The present paper embodies the results of a study of various questions 

 of geology and manner of formation of the zeolites and associated sec- 

 ondary minerals which are found within the area of Watchung basalt 

 mentioned. The work has been carried out under the direction of the 

 Geological Department of Columbia University, and the microscopic 

 studies of rock sections have been made in the petrographic laboratory of 

 that institution. The writer takes the greatest pleasure in acknowledging 

 his sense of deep obligation to the members of the Geological Department, 

 Professor Kemp, Professor Berkey and Professor Grabau, for their kind- 

 ness and assistance throughout in guidance and suggestions. 



The chief features which will be considered in the paper are the 

 geologic conditions which gave rise to the formation of the secondary 

 minerals and the order of succession of the various species as determined 

 by petrographic methods, and in connection with this the results attained 

 will be interpreted, so far as has been found possible, in the light of the 

 laws of physical chemistry. The application of this branch of science in 

 its modern aspects to the problems of the mineralogist and petrographer 

 is at the present time at a most interesting stage, where the applicability 

 and value of the principles are perceived, but application to specific cases 

 has been slight. 



I. Geology of the Kegion 



CONDITIONS OF TRIASSIC DEPOSITION 



An understanding of the major features of the geologic history of the 

 region under discussion for a short period prior to the extrusion of the 

 First AVatchung basalt is essential for a comprehension of the processes 

 which resulted in the formation of the secondary' minerals. There has 

 been some lack of agreement among different observers as to the interpre- 

 tation of certain features of Triassic history. Earlier views were influ- 



