Campbell — Rogers's Geology of the Virginias. 361 



In subsequent Reports, and in his notes on the geology of 

 the Chesapeake & Ohio and Yirginia Midland Railways he rec- 

 ognizes the rocks of this same region as primary or Archaean. 

 We do not call attention to this change of view for the purpose 

 of throwing any discredit upon the author's conclusions, but 

 rather to indicate his honesty of opinion in changing where 

 subsequent observations pointed out his error. In the subse- 

 quent Reports, made from more careful and detailed explora- 

 tions, there is left but little room for such changes, while the 

 general accuracy of his conclusions is remarkable for that early 

 period. 



Prof. Rogers's classification of the primary rocks is about as 

 distinct as any that has yet been made, but the territorial 

 limits given to these general classes, or rather their outcrop- 

 pings, fall far short of covering the whole area occupied by 

 them. Still he is correct as far as he goes in the following 

 paragraphs ; if his definitions are accepted. 



" Granite (la.) — An unstratified or igneous rock generally 

 found inferior to or associated with the oldest stratified and 

 metamorphic rocks, and sometimes penetrating them in the 

 form of veins, and of dykes or walls rising in the midst of them. 

 ... A true unstratified granite, though extensively displayed 

 in some parts of our southern district, is by no means of com- 

 mon occurrence. As an example of it I would cite the belt of 

 whitish, hard, solid rock, extending from a little distance east 

 of Little Falling River in Campbell county (S.B. corner), with 

 a breadth of between one and two miles across Staunton 

 River in the neighborhood of Brookneal," (pp. 287-88). Re- 

 ferring to exposures of gneiss and gneissoid granite near Rich- 

 mond and Petersburg, he says : " We observe at many expos- 

 ures, veins of granite and syenite penetrating the gneiss, and 

 in some instances in such extent as to present large protruding 

 masses, or broad surfaces of the granitic and syenitic rocks 

 above, as may be well seen at several points along the James 

 River canal (now the Richmond & Allegany railway), and per- 

 haps still more readily at the rugged exposures adjoining the 

 mills on both sides of the Appomattox at Petersburg," (p. 457.) 



" Gneiss (la.) — A stratified rock composed of the same ma- 

 terial as granite, having a laminated texture. . . . Grneiss rocks 

 are in extensive use as building material in nearly all of the 

 Atlantic states. In the southern districts they have been quar- 

 ried below Columbia and between that point and Lynchburg. 

 ... A wide belt of micaceous and feldspathic gneiss traverses 

 Albemarle, Nelson, Amherst, Bedford, Franklin and Patrick 

 counties, presenting frequent beds of granite and syenite, the 

 latter more largely developed in proceeding toward the south- 



Am. Joue. Sci.— Third Series, Vol. XXX, No. 179.— Nov., 1885. 

 23 



