480 



PROCEEDINGS OF THE NATIONAL MUSEUM. 



vol. 59. 



graphic and other characters of the several minerals, with a discus- 

 sion of their paragenesis and origin. Several shorter preliminary 

 papers on various subjects relating to the locality have already been 

 published. It was planned to make the present paper final and 

 complete, but the crystallographic data on the datolite has assumed 

 such proportions that it has been decided to reserve discussion of 

 other subjects for another and final paper to be presented shortly. 

 The following discussion of the crystallography of the Westfield 

 datolite is based upon a very thorough acquaintance with the mate- 

 rial. While at the quarries these specimens were selected with the 

 view of securing as many variations in habit as might occur. Speci- 



Fig. 1.— Stereografhic projection showing the common forms occurring on datolite, plotted 

 in the Dana orientation. The symmetry is expressed by the falling of the forms in ver- 

 tical ZONES. 



mens from unusual situations were especially sought, and all of the 

 quarries were systematically sampled at various times while work 

 was in progress. The United States National Museum had already 

 acquired several excellent exhibition specimens of this datolite 

 which were available for study, and in addition to these and the 

 collection made by the writer a lot of some 35 specimens collected 

 over a period of several years following the opening of the quarries 

 was secured by exchange from Mr. William L. Fitts, of Springfield. 

 The entire stock of this material held by Ward's Natural Science 

 Establishment was also borrowed for study. From this large number 

 of specimens about 200 crystals were selected for study, and after 

 numerous preliminary measurements about two-thirds of this number 

 were eliminated as duplicates. The series of about 50 crystals 

 which was completely studied represents a concentration containing 



