722 DEPARTMENT OF THE INTERIOR 



2 GEORGE V., A. 1912 



granite.' The name has since been commonly used for bodies of intrusive rock 

 with the general characteristics of stocks, but of much larger size than is gener- 

 ally attributed to stocks or bosses. This latter use is, moreover, rarely associ- 

 ated directly with any particular theory of intrusion. There is pressing need 

 for such a term signifying these large bodies, and one that will not commit 

 the field worker to any theory of origins. The later use of the term ' batholith ' 

 is therefore to be commended, as it renders that term safe in actual field des- 

 criptions where these cannot be accompanied with certain proofs that the 

 Durchschmelziing theory is there applicable. In the proposed classification of 

 intrusives the term ' batholith ' will have the meaning just noted. 



A simple batholith is one composed of material intruded in one period of 

 intrusion. 



A multiple batholith is one composed of material demonstrably intruded 

 in two or more periods of irruption, the material having been derived from the 

 same kind of magma. 



A composite batholith is one composed of materials demonstrably intruded 

 in two or more periods of irruption, the materials being originally derived from 

 two or more kinds of magma. 



A multiple or composite batholith may thus be in part made up of stocks. 



Magmatic differentiation or other influences may render heterogeneous the 

 material composing a simple batholith; or each member of a multiple or a 

 composite batholith. 



No author has attempted to fix a lower limit to the areal dimensions of a 

 batholith. Since there is no certain distinction either in form or relations 

 between stocks and batholiths, an arbitrary limit may be set between the two on 

 the score of areal extent. In the 1905 paper it was proposed that the upper 

 limit in the size of stocks be placed at 200 square kilometres. A further study 

 of the literature has made it seem advisable, in order to conform to actual 

 usage, to make the limit no higher than 100 square kilometres. Any mass with 

 the stock relations, but of greater area than 100 square kilometres, is, accord- 

 ingly, a batholith. 



Proposed Classification. 



The following table gives the proposed classification, as slightly enlarged 

 from that in the 1905 paper: — 



A. — Injected masses. 



I. Concordant injections {injected along bedding planes). 

 1. Intrusive sheets, homogeneous and differentiated. 



(a) Sills. 



(1) Simple. 



(2) Multiple. 



(3) Composite. 



(b) Interformational sheets. 



