Cincinnati Society of Natural History. 



since similar granites farther south, which have not been so 

 squeezed, are relatively free from epidote. Nevertheless, the 

 chemical composition of the feldspar seems, on the whole, to 

 have had more influence on this particular form of alteration 

 than the external forces acting upon it. Extreme dynamic 

 action seems rather to have hindered than favored the forma- 

 tion of epidote, as is seen by comparing the Rowlandville 

 with the more intensely foliated Port Deposit region ; while 

 other Maryland granites whose feldspar is mainly orthoclase, 

 contain little or no epidote, even where they were more 

 sheared than at Rowlandville. In this case here under con- 

 sideration the feldspar is principally plagioclase, and this 

 cause more than any other seems to account for the epidote 

 development. The undoubted causal relation which exists 

 between the zonal structure of the feldspars and their altera- 

 tion, whereby these zones richest in lime have been most com- 

 pletely changed to epidote, also greatly favors this view. 



Becke, in his recent work quoted above, shows that the 

 outer zone of his tonalite feldspars is always albite. This 

 seems in the rocks here described also to be the case, and 

 this outer zone is almost entirely free from the secondary 

 epidote. 



In many localities physical conditions favorable to epidoti- 

 zation on a grand scale are known to have obtained, where 

 the material acted upon was suited to this alteration. In 

 other localities, on the contrary, quite the same material was 

 changed in an altogether different manner. The operation 

 of such conditions favorable to epidotization is nowhere 

 better seen than in the basic volcanic rocks of the Blue Ridge 

 in Maryland. Similar conditions must also have once pre- 

 vailed in the Rowlandville area, while the composition of the 

 feldspar in the granite furnished material in which this change 

 readily progressed. 



The change of feldspar into epidote has often been men- 

 tioned in the literature, and good lists of such references are 

 given by Inonstranzeff,* Roth,f and Schenck.J 



Epidote Needles. — The epidote which has been described in 

 the foregoing paragraphs as replacing feldspar, also occurs in 



-Studien iiber Metamorphosirte Gesteine in Gouvernment Olonez, p. 188, 187( . 

 tAllgemeine and Chemische Geologic Vol. I, p. 310, 1879. 

 |Diaba.se des Oberen Ruhrthal, p. 28 1884. 



