CLASSIFICATION OF IGNEOUS INTRUSIVE BODIES 487 



good observer always feels the pressure of the category. If his 

 classification be systematic, his observing power is quickened, his 

 report enriched; if his classification be that in general use, his des- 

 criptions will be of the greater service to the science. 



The purpose of this paper is to present certain of the current 

 definitions and classifications of intrusive bodies; from the defini- 

 tions and classifications to attempt the deduction of the various 

 principles underlying them; and, finally, to offer for discussion a 

 classification which shall aim at a systematic and consistent use of 

 the principles which seem best adapted to the case. As far as possible, 

 these principles are the same as those already in common use among 

 leading geologists. 



FORMER CLASSIFICATIONS 



A few representative classifications of igneous intrusive bodies 

 will serve to show the range of types recognized by recent authors. 



I. Sir Archibald Geikie, Text-book of Geology (4th ed., 1903), Vol. II, p. 722: 



1. Bosses (stocks). 



2. Sills, intrusive sheets. 

 Variety: laccolith. 



3. Veins and dykes. 



Varieties: contemporaneous veins, segregation veins, multiple dykes, 

 compound dykes. 



4. Necks, 



II. T. C. Chamberlin and R. D. Salisbury, Geology (1904), Vol. I., pp. 476, 477: 



1. Dikes. 



2. Necks or plugs. 



3. Sills. 



4. Laccoliths. 



5. Bysmaliths. 



6. Bathyliths. 



III. F. Zirkel, Lehrbuch der Petrographie (1893), Vol. I, p. 539: 



1. Gange. 



2. Lagergange. 



3. Gangstocke. 



4. Apophysen. 



5. Stocke. 



6. Intrusivlager. 



7. Lakkolithen. 



