FREE INSTITUTE OF SCIENCE 
MINERALOGY OF THE NEWARK GROUP IN PENNSYLVANIA, 
METAMORPHISM OF THE SEDIMENTARIES 
NE of the principal objects of the present study was, as mentioned in 
the introduction, the determination of the character of the change in 
color so frequently observed in the metamorphosed sediments of the 
Newark Group. That the bright red color which constitutes such a striking 
and characteristic feature of these rocks is produced by a small percentage 
of ferric oxid is generally recognized. But no attempt appears to have been 
made to decide whether the gray color developed in the altered rocks is due to the 
removal of this iron, to its reduction to a lower state of oxidation, or to its 
entering into new minerals without change of state. 
It seemed first desirable to ascertain the composition of the unaltered shale 
and for this purpose a sample was obtained from the exposure on the hillside 
west of Antietam Creek, two feet below the base of the extrusive sheet. Stand- 
ard methods of analysis were employed, chiefly those of Dr. Hillebrand’s papers;* 
the ferrous iron was determined by the Pratt method, as modified by Mr. R. B. 
Gage,’ and the water by loss on ignition, with correction for the carbon dioxid, 
obtained directly. In order to gain some idea as to the character of the minerals 
present, the sample was first boiled with 20% hydrochloric acid, and the solution 
and residue analyzed separately. The following results were obtained: 
SOLUBLE IN НСІ. INSOLUBLE IN НСІ. TOTALS 
V 0.56 75.62 76.18 
AO paa Wis aldea UN 0.48 5.68 6.16 
h үз 0.92 4.64 
ee 1. 10 EN 1.10 
KR AN 4.72 trace 4.72 
IMO) NL ER e trace none trace 
AO NS 4.40 MER 4.40 
ADO PU cade си SOM idus 0.54 
КОО glued và «s vir EE DUM TO 
99.84 
From these data the mineralogical composition of the rock was readily 
calculated. The silica is evidently present in two forms, as free quartz and in 
combination with alumina as kaolinite, a small amount of this latter mineral 
having dissolved in the acid, although most of it is insoluble. The ferric oxid 
appears to be all in the form of hematite, the insoluble portion representing 
particles enclosed in the cracks in the sand grains. The ferrous oxid was 
