A. W. Jackson — Nomenclature of Crystalline Bocks. 113 



Another cause for a portion of the retardation may be con- 

 sidered to be the sluggishness in action of the summit barome- 

 ters, or again, to be" the slowness with which the air at the 

 maxima and minima of pressure would enter and leave the 

 room where the observations were made, undoubtedly less 

 accessible to the atmosphere at the summit than at the base. 

 These last two causes, however, would be of little consequence 

 in producing the results noted. 



May we not be enabled, by a sufficient number of carefully 

 conducted ol ling over a year, at the base and 



along the side of Pike's Peak or some other isolated mountain, 

 to determine the cause of the diurnal range of air pressure, 

 which has been characterized as the most persistent of all 

 meteorological phenomena and never as yet satisfactorily 

 accounted for? If the above discussion assigning varying 

 temperature as the cause of the apparent retardation of the 

 axis of a "low" at high stations prove satisfactory, it will also 

 show the great difficulty which inevitably attends any attempt 

 made in comparing pressures observed at elevations above the 

 earth with those observed at the same time at sea-level. 



Acknowledgment is due to Professor Abbe for Bug 

 in the final construction of this paper. 



INTRODUCTION. 



The objects of the present paper are, first, to suggest the com- 

 plete separation of rocl 



and, second, to investigate and to establish, as far as may be, the 

 principles upon which any system of nomenclature for the mas- 

 sive crystalline ro -ks si <>uM he based. Throughout my paper 

 the term " nomenclature" is to be understood as referring to the 

 names of the rocks themselves and not of the larger groups 

 recognized in rock-classifications. 



The existing confusion in rock-nomenclature is due to sev- 

 eral causes, not the least of which is tin- admission of classifica- 

 tion as a controlling feature in nomenclature, and the tendency 

 seems to be more and more in this direction. This \ 

 even directly advocated in a recent able work (Dutton, "Geol- 

 ogy of the High Plateaus of Utah," Chap. iv). Its general rec- 

 o'j'nition ciu nnh result di-a-tu.u-l\ to the science. The true 

 function of present systems of classification is to express rela- 

 tions between the objects classified. The true function of a 

 system of nomenclature is to furnish each of these objects with 

 Am. Jour. Sci.-Thied Series, Vol. XXIV, No. 14G.-Aic>/-r, lW.\ 



