FREE INSTITUTE OFYSCIENCE А 
MINERALOGY OF THE NEWARK GROUP IN PENNSYLVANIA 
tered kaolinite, it can not all be this mineral, for the water is too low by over 
one per cent. That some of the supposed magnetite might be an iron spinel 
(hercynite ?) is not impossible, but in the absence of any means of ascertaining 
this, the calculation of the mineralogical composition has been made on a 
magnetite-kaolinite-epidote basis, the last being assumed to have Fe:Al = 1:2, 
for convenience, and gives: 
irt i ! 64.25 
Epidote; MCa pes O AERE QU 14.07 
EAN E ẽ q)“m Vg! veg UN En 17.00 
ip Ketao Kena iyn MD eno ate o ea „„ A k a c dices 2.47 
la ge e ОАЕ 2121 
100.00 
The gray portion behaved in an entirely similar manner; its chemical 
composition was: 
SOLUBLE IN HCl. INSOLUBLE IN НСІ. TOTALS. 
S OP PIDE 0.20 77 DA 77-34 
ALONE S Re cal 2.57 7.28 9.85 
Ге BE ena 1.37 4.34 5.71 
DEN RR N Quy NO rabo 
BLEND IRR AGED NM IR 1.26 200 4.46 
VID D PARS И prati tutum UL us 0.05 0.05 
H e ПЕ x EN бз 0.44 
RA d XA 0.98 
99.93 
And the minerals present may be calculated as: 
Gr 8 62.81 
ee ß NA Sí UU 19.10 
O o a ee 14.50 
Наша S D (0 A cce 8 0.07 
NUIT en ni Ке en UA Led: 282 
100.00 
Comparison of the mineralogical compositions of these different samples 
justifies the conclusions that the chief difference between the altered and unaltered 
shales consists in the state of combination of the iron and calcium; THE INDURA- 
TION PRODUCED BY THE IGNEOUS ACTION BEING PRINCIPALLY DUE TO THE 
CHANGE OF CALCITE INTO EPIDOTE, WHILE THE LOSS OF COLOR 18 NOT DUE TO 
REMOVAL OF IRON, BUT IN PART TO THE ENTRANCE OF THAT ELEMENT INTO THE 
EPIDOTE MOLECULE, AND IN PART TO THE CHANGE OF HEMATITE INTO MAGNETITE. 
