REPORT OF THE CHIEF ASTRONOMER 723 



SESSIONAL PAPER No. 25a 



2. Laccoliths, homogeneous and differentiated. 



(1) Simple. 



Symmetric. 

 Asymmetric. 



(2) Multiple. 



(3) Composite. 



(4) Interformational. 



3. Phacoliths. 



II. Discordant injections (injected across bedding planes). 



1. Dikes, homogeneous and differentiated. 



(1) Simple. 



(2) Multiple. 



(3) Composite. 



2. Apophyses or tongues. 



3. Bysmaliths. 



4. Necks. 



5. Chonoliths. 



Ethmoliths. 



B. — Subjacent masses. 



1. Stocks and bosses, homogeneous and differentiated. 



(1) Simple. 



(2) Multiple. 



(3) Composite. 



2. Batholiths, homogeneous and differentiated. 



(1) Simple. 



(2) Multiple. 



(3) Composite. 



The classification can lay no claim to completeness, but it suffices to point 

 to the real crux of the present situation in igneous geology. In spite of some 

 uncertainties regarding some types the modes of intrusion for the injected 

 masses are fairly well understood. It is quite different with the vastly larger, 

 subjacent masses, from which many of the bodies of the first group have been 

 derived, and of which they are to be regarded as satellites. The problem of the 

 batholithic form and relations is, therefore, the difficult prelude to the complete 

 understanding of the injected bodies whether considered with respect to petro- 

 geny or to the dynamics of their injection. If the batholithic problem is solved 

 we shall have essential facts regarding the origin of magmas. For this reason 

 a somewhat detailed discussion of the methods of batholithic intrusion may well 

 anticipate the study of magmatic differentiation. The discussion will be based 

 on the idea of a primary acid earth-shell and a basaltic substratum. " It will be 

 seen that a multitude of field and laboratory observations agree in supporting 

 this conception as well as the hypothesis of abyssal injection. The conclusion 

 will be reached that batholiths are the more or less chemically-modified tops 



25a — vol. iii — 47 



