84 



PROCEEDINGS OF THE NATTONAX, MUSEUM. 



VOL. 66. 



sequence of minerals in the zeolite assemblage from first to last prob- 

 ably resulted from gradual decrease of temperature and pressure away 

 from the source of the solutions. Toward the end of the series the 

 solutions apparently had lost then- vigor and exercised only a mild 

 alteration effect upon the rock intersected by the sheared zones, 

 with some kaolinization and sericitization of the feldspar and staining 

 of the pyroxene by chloritic material. There can exist no reasonable 

 doubt that the agency which deposited all of the vein minerals was 

 water and that this water was magmatic, the final product of the 



consolidated diabase, ascending (or 

 traveling laterally) through fissures in 

 the previously consolidated material. 

 This conclusion is in entire agree- 

 ment with the excellent statement of 

 Lewis " of the mode of origin of the zeo- 

 lites and associated minerals of the 

 New Jersey localities. 



In the quarry at Goose Creek the 

 only veins seen are contained in the 

 pa,rent diabase. In a quarry at Lees- 

 burg in limestone immediately above 

 the sill the veins penetrate the Trias- 

 sic limestone fanglomerate and have 

 deposited much calcite and datolite 

 with some barite, apophyllite, etc. 

 The minerals of this Leesburg quarry 

 are to be described in another paper 

 which is now in preparation; a third 

 paper in the series will describe the 

 phenomena observed at Dickerson, 

 Maryland, where the diabase has pene- 

 trated and altered Triassic shale. 



The total net effect of the hydro- 

 thermal alteration of the normal dia- 

 base can not be definitely arrived at 

 in the absence of an analysis of the altered material. The effect along 

 the diopside seams probably has been a considerable addition of soda 

 with removal of lime and iron. It seems probable that the alkahes 

 and at least part of the silica were originally contained in the solu- 

 tions but the later minerals of the series in the veins may in large 

 part be made up of materials extracted from the adjacent rock. 

 Thus much of the lime of the apophyllite, prehnite, datolite, and 



Fig. 32. — Calcite. Habit of a single 

 white crystal observed resting on 

 prehnite. 



" J. Volney Lewis. Origin of the secondary minerals of the Triassic trap rocks. New Jersey QeoL 

 Survey Bull. 16, Ann. Rept. for 1914, pp. 45-49, 1915. 



