486 REGINALD A. DALY 



used to describe them. That precision depends on definition. 

 Scientific definition necessarily means classification. 



Neither in the definition nor in the classification of igneous intru- 

 sive bodies is there at present unanimity or consistency among geolo- 

 gists. The same author defines "dike" or "sheet" or "batholith" 

 in quite different ways on different pages. Of late years "laccolith," 

 "boss," "stock," and practically every other term referring to igneous 

 intrusions, have from different writers respectively received definitions 

 varying in essentials. In several cases the difference of usage has 

 sprung from the subjective influence of theories of intrusion. Some 

 of the most recent definitions of older terms have thus become too 

 intensive in meaning to fill the needs of the great body of field workers 

 who are still in the wholesome attitude of mind that forbids the final 

 adoption of any theory of intrusion for many important igneous 

 bodies. 



The writer believes that a comparatively full classification of 

 igneous intrusive bodies is needed. The general adoption of a con- 

 sistent, well-defined scheme of types — a scheme as complete as 

 possible, but elastic enough to permit of new types — would tend to 

 make field descriptions more scientific than many of them are at 

 present. Such general adoption would mean a gain in precision, 

 the soul of scientific writing; a gain in the ease with which a paper 

 descriptive of igneous intrusions would be understood; and an 

 economy of words induced by the employment of terms of definite, 

 precise meaning. The filling-out of the scheme of classification to 

 an extent quite beyond that now prevailing in standard text-books 

 of geology should further have the effect of sharpening the eyes of 

 the field observer. He may perhaps not be content to describe a 

 given granite intrusion as simply a "mass," or an "area," or an 

 "outcrop," if it be possible by the study of its contents to indicate 

 the real form and relations of the granite body. The use of the 

 term "mass" in that sense is often excellent because of the apparent 

 impossibility of determining the true shape of the granite body; 

 but such justifiable employment of the term implies that that par- 

 ticular body cannot as yet be thoroughly classified. A rather negative 

 name has in such a case a distinct value. Of yet greater value is 

 the positive reference of intrusive bodies to definite categories. A 



