> 
COMPOSITION OF METAMORPHOSED SEDIMENTS 197 
with the data at present available cannot be determined. For 
this reason the criteria cannot be applied automatically without 
the exercise of judgment and discretion on the part of the investi- 
gator. It should be especially remembered that if the rocks under 
investigation have been subjected, either before or after the develop- 
ment of their foliated structure, to severe igneous or hydrothermal 
TABLE I 
I II Til 
SyQac' crake otorekeeNrake Slate GE OAI ORE ene 57-35 49.59 61.62 
ANIAO)s Soteothic 2vo%0o3 tie atc cree, Oe 16.2 14.91 19.98 
Fe,0, “ig. Gxt O8G BNC 0 GO ec ool EG be Enc CREE Eo Boiss S52 3.46 
TPO) 5 1c: 0 cede bib nich dg Re ae 4.306 10.46 257 
INIGEO), Ge6.6 oc Se cROe ODD 2G Care cae ee nee 2.41 2.02 Th 12 
(Or OPP i tee ees wean 5.66 E00). | 62 
INGO, os eee eee ARS FOR’ 1.78 
Don d pe B68 8 OB ee ee 3530 asi 35 
TRL{O) 3 A Sil oleae ee ges 515 16 21 
[ELLOS aciotara cio e Sater aoe ea ane .70 37 2 AN 
UWO). 3 Se Seele a bes. ere een ec ceo TO7 moe | 56 
AO ree eT UT EP ees Shite Go tenale Sates eat tee none 
(CHO eae ae 6S ee SNe ee eee 46 9.40 
IPAQ) auseccd eB Ghd HHS rene Cnc nee ae ea 570 47 
INTO) 5 aula ones 8 Behe ocr one Seen Gre eto een nea eee 12 1.10 
(OiiIESAS 5, eRe tate epee aya eget eee Re ee 2 A3 
MING ticle ete Maen carter sien dad busvalfoni 100.55 100.06 99.62 
I. Fresh diorite porphyry 25 feet from vein, Wellington mine, Breckenridge, Colo. W. T. Schaller, 
analyst. 
II. Altered diorite porphyry ro feet from vein, Wellington mine, Breckenridge, Colo. W. T. Schaller, 
analyst. 
III. Pinal schist, Ray district, Arizona. Analysis made for Dr. F. L. Ransome by R. C. Wells. 
metamorphism, the criteria are not applicable, for such meta- 
morphism involves important additions and losses of material. 
For example, analyses I and II of Table II taken from Dr. Ran- 
some’s report on the Breckenridge district, Colorado, show that in 
the hydrothermal metamorphism of a diorite porphyry there has 
been a much greater depletion in lime than in magnesia and that 
there has been an accession of potash and loss of soda, yielding a 
0 Ne?) 
rock in which the double relationship and 
MgO> CaO 
‘tF. L. Ransome, “Geology and Ore Deposits of the Breckenridge District, 
Colorado,” Prof. Paper U.S. Geol. Surv. No. 75 (1911), p. 90. 
is present. 
