464 WHITMAN CROSS 



proposed application of his asserted principle to the construc- 

 tion of a system, and no further portions of the projected work 

 have appeared. It is plain that the basis of Wadsworth's 

 conception is contrary to known facts of petrogenesis. A 

 direct contribution to petrographic system is afforded by the 

 proposition made by Wadsworth to group terrestrial and mete- 

 oric masses together, applying to them a single system and 

 nomenclature. The descriptive portion of the published work is,, 

 in fact, mainly occupied with discussion of meteorites rich in 

 iron. Wadsworth thus goes a step further than von Lasaulx, 

 who treated meteorites in an appendix to his discussion of ter- 

 restrial rocks (p. 455 ). 



It is hoped that the trend of the evolution of systematic 

 petrography during the earlier portion of the microscopical era 

 has been fairly indicated in the preceding pages. The tendency, 

 most natural under the circumstances, was to overestimate the 

 systematic importance of some of the discoveries made through 

 the microscope, and to slight other, more fundamental, prop- 

 erties or relations of rocks. Many new rock names were 

 proposed and usage became fixed and extended in directions 

 where it had never been well grounded. Protests against the 

 tendency of the times were numerous, and especially from the 

 geologist's standpoint. Many of these protests were of little 

 influence, because based upon imperfect appreciation of the situa- 

 tion ; others were far too conservative in spirit. 



/. D. Dana, 1878. — As an example of the conservative 

 geologist's view at this time may be cited the discussion of 

 petrographic system by J. D. Dana in an article published in the 

 American Journal of Science in 1878 under the title "On some 

 Points in Lithology." 1 This article refers to the Mikroskopische 

 Physiographic of Rosenbusch, and to other recent works, and 

 may be taken as expressing the author's view of petrography at 

 the stage of its development just reviewed. 



Lithology, according to Dana, is charged with the descrip- 



1 Amer.Jour. Sci., 3d ser., Vol. XVI, p. 335, 1878. 



