CONTRIBUTIONS TO THE MINERALOGY OF THE 
NEWARK GROUP IN PENNSYLVANIA 
INTRODUCTION 
HILE the Newark Group of the Eastern United States has at- 
tracted considerable attention from geologists during the past few 
years, there is still a lack of knowledge concerning certain of its 
features. In 1907, while engaged ina study of the copper deposits of this 
terrane, the writer had occasion to inquire into the nature of the change from a 
red to a gray color so frequently observed in the sediments where affected by 
igneous rocks, and into the origin of the secondary minerals occurring in the 
cavities in the latter. Search through the literature failing to reveal any satis- 
factory data upon these points, a paper on the copper ores was prepared and 
published without including reference to them, but later, when opportunity 
presented itself, a study of them was undertaken, and its results are recorded 
in this paper. 
In the course of the work on the copper deposits it had appeared desir- 
able to examine as many of the Newark traps as possible, and in the vicinity 
of the town of Jacksonwald, Berks County, four miles southeast of Reading, 
the rocks were found to present an unusually favorable opportunity for study. 
Here was discovered the only occurrence of extrusive basalt as yet observed 
within the boundaries of the State; and here an intrusive mass was found to 
be so closely associated with this extrusive one that a direct comparison of 
their structural features and their metamorphic effects upon the surrounding 
sedimentaries could be made; while the relations of the secondary minerals 
developed in the extrusive rock seemed capable of throwing some light on 
their origin. 
To Professor Amos P. Brown, under whose direction this study has been 
carried out, the most cordial thanks of the writer are hereby extended, in appre- 
ciation of his ever-ready advice, encouragement, and assistance, without which 
this paper would never have been prepared. 
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