42 The American Geologist. January, 1895 
Grimsley, has been the extensive development of epidote. As 
stated by him, the physical conditions particularly have been 
exceptionally favorable to the formation of this mineral. It 
occurs everywhere in the Rowlandville area as a prominent 
metamorphic product, assuming varietj^ of forms, sharply 
outlined crystals, rounded grains and hair-like needles, and 
developing in all of the original constituents alike. The pro- 
duction of epidote to such an unusual degree is manifestly 
one of the chief results of the metamorphic action, and hence 
the consideration of the mineral has been given in full detail. 
Now, the original Rowlandville rock w^as evidently a normal 
granitite or biotite granite having the common hypidiomor- 
phic, structure and carrying unusually large proportions of 
plagioclase. In places it is thought that it may have also 
contained some original muscovite. As already stated, epi- 
dotization has been carried on on an extensive scale. It is 
most marked in the feldspars. In the perfectly fresh rocks, 
those which have suffered no effects through meteoric changes, 
the formation of the mineral, it must be admitted, must cer- 
tainly be metamorphic rather than the result of weathering, 
as has been stated from time to time. All degrees of replace- 
ment of the feldspar by epidote occur, from crystals in which 
only an occasional grain of the latter mineral has originated 
to those in which almost complete pseudomorphism has taken 
place. Whenever there is a small amount of epidote, crystals 
oE this mineral, with sharp outlines and of the usual mono- 
clinic habit, are of frequent occurrence; but as the amount 
increases the different crystals unite into larger masses with 
irregular boundaries. Another interesting observation which 
was made concerning the Rowlandville granite was that the 
epidote had no special tendency to develop in or near cracks 
in the feldspars, but that whenever the latter crystals showed 
pressure efftjcts little or no epidote was formed. Another 
suggestive observation is that the epidote frequentl}^ devel- 
oped in certain zones in the feldspar crystals, in many cases 
both the interior and exterior of the feldspars remaining un- 
changed, ('onsidering the well known fact of zonal variations 
in the chemical composition of feldspar crystals which has so 
well been worked out both by Hopfner* and by Becke,f who 
*Neues .Jahrbuch. C.eol., Min. u. Pal., 1881, 2 Haft, p. 182. 
fTschurmak's min. luid pctro Mitth., xiii, Band. p. 414, 1898. 
