r 



196 WATSON AND CLINE ROCKS OF THE BLUE RIDGE REGION 



The results presented in this paper are based on field and laboratory 

 investigations of the igneous complex which forms the central core of the 

 northern and middle Blue Ridge region and the adjacent portions of the 

 extreme western margin of the Piedmont Plateau, undertaken at brief 

 intervals during the past ten years. The scope of the paper is limited to 

 a petrographic study of this igneous complex, since a complete discussion 

 of the Blue Ridge igneous complex can not be attempted in advance of a 

 thorough investigation of the field relationships. The , principal claim 

 for this study, therefore, is as a contribution to the petrography of the 

 Blue Ridge geology. 



Previous geologic Work 



Probably the first reference to the syenites of the Blue Ridge in Vir- 

 ginia was by Prof. William Barton Rogers 2 in his annual reports on the 

 Geology of the Virginias from 1835 to 1841. He refers to the occurrence 

 of syenitic rocks at various places in the Blue Ridge, notably in the James 

 River and Tye River gaps, and makes special reference to the pronounced 

 porphyritic texture of the syenite in Tye River Gap. 



During his early work in Virginia Prof. William M. Fontaine devoted 

 considerable time in the field to study of the Blue Ridge syenites. Only 

 occasional reference is made to their occurrence in his publications, yet 

 the degree to which they attracted his attention is shown by the large 

 collection of the rocks which he made from different parts of the Bine 

 Ridge and adjacent portions of the Piedmont Plateau. These collections 

 are preserved in Brooks Museum at the University of Virginia and have 

 been freely used in this study. 



In 1884, Professor Fontaine sent to the United States National Mu- 

 seum specimens of unakite from Milams Gap, in Page and Madison 

 counties, Virginia, and later, in 1913, specimens of the associated syenite 

 This led to the first petrographic description of these rocks in 1904 by 

 Mr. W. C. Phalen, 3 who designated the syenite of the Page-Madison 

 counties area as hypersthene akerite because of its similarity to the 

 akerites of Norway described by Brogger. 



In 1894, Mr. Arthur Keith 4 mapped the syenite occurring southwest of 

 Front Royal along the extreme western side of the crystalline belt as 

 granite, six varieties of which he distinguished and described in the Bine 

 Ridge region. Keith's description of one of the varieties follows: 



2 See a reprint of annual reports and other papers on the geology of the Virginias by 

 William Barton Rogers, 1884, 832 pages. 



3 W. C. Phalen : A new occurrence of unakite. Smithsonian Miscellaneous Collections, 

 vol. 45, 1904, pp. 306-316. 



4 Arthur Keith: Geology of the Catoctln Belt, Fourteenth Ann. Rept. U. S. Geol 

 Survey, 1894, part 11, pp, 285-395, 



