THE CLASSIFICATION OF IGNEOUS INTRUSIVE BODIES 1 



REGINALD A. DALY 

 Ottawa, Canada 



CONTENTS 

 The Need for a Classification. 

 Former Classifications. 



Definition of Terms Descriptive of Intrusive Bodies. 

 Principles of Classification. 

 Proposed Classification of Igneous Intrusive Bodies. 



THE NEED FOR A CLASSIFICATION 



At the present time geological science is engaged with no general 

 question more widely and thoroughly discussed than that of the 

 origin of the igneous rocks. The elaborate chemical studies of those 

 rocks, the many new classifications of rock species, the modern 

 experiments in the synthesis of natural silicates, and the experiments 

 on the physical and chemical properties of molten silicates, have as 

 their chief end the demonstration of the facts upon which a stable 

 theory of rock genesis can be founded. 



All such studies must be pursued with constant reference to the 

 actual occurrences of igneous rocks in nature. Petrology is dependent 

 upon, knit together with, field geology; the heart of geological 

 philosophy is petrology in its broad sense. On the chemical side 

 the laboratory observations of rock-analysts have been rated as 

 "superior" (excellent, fair, or good) or as "inferior" (poor or bad). 

 Similarly, field observations can be rated as superior or inferior 

 according to the fulness and accuracy with which they supply the 

 data from outdoor nature. Of those facts none is of more impor- 

 tance to petrology than the mode of occurrence of igneous rocks. 



The field information required for the great group of the igneous 

 intrusives relates to their shapes, sizes, and methods of intrusion. 

 The statement of field facts depends on the precision of the terms 



1 Published by permission of the Canadian Commissioner, International Boundary 

 Surveys. 



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