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University of California Publications in Geology [Vol. 8 



The relations of the Boulder mass to the remnants of its roof are 

 interesting in this connection. These remnants in the more central 

 parts of the granitic area consist chiefly of andesite and latite with 

 some patches of Cretaceous sediments. 20 The distribution of these 

 remnants is such as to indicate no doming of the roof, as Sales on 

 other grounds has already pointed out. It is clear that, as Weed 30 

 remarks, "the granite must have either penetrated between the ande- 

 sites and the base upon which they rested or removed the basal rocks, 

 whatever they were." In the first of these two contingencies the 

 intrusive mass is a laccolith ; in the second it is a batholith. If it be 

 the latter, there is no necessary genetic relationship between the syn- 

 clinal structure and the development of the batholith. If it be a 

 laccolith without a domed roof, then the floor must have sagged to 

 accommodate the injection. The actual fact of the general synclinal 

 structure is, therefore, more suggestive of laccolithic than of batho- 

 lithic structure, even though the suggestion appear to turn the profile 

 of the typical small laccolith upside down. 



Metamorphism. — Termier 31 has offered us a criterion for discrimi- 

 nating between batholiths and laccoliths on the basis of the intensity 

 of the metamorphism manifested by the rocks adjacent to the intru- 

 sive mass. This test is unfortunately difficult of application for three 

 reasons : ( 1 ) It is a quantitative test in which the quantities are not 

 definitely specified, so that much is left to individual judgment and 

 experience; (2) it is based upon the notion that even large injected 

 masses do not approach small batholiths in the intensity of the meta- 

 morphism which is engendered on their periphery; and (3) it ignores 

 the possibility that a batholith may in the normal course of its growth 

 swallow up the original zone of intense metamorphism by stoping and 

 resorption, and by mere distension, without injection, give rise to a 

 succession of metamorphic zones each feebler than its predecessor, so 

 that the last zone, that formed immediately antecedent to solidifi- 

 cation, may differ greatly in intensity from the first formed zone. 



Notwithstanding these limitations upon Termier 's criterion, it is 

 nevertheless true, in general, that batholiths have induced wider zones 

 of more intense metamorphism than have even large laccoliths. The 

 character of the contact zone is probably a function of the depth of 

 the molten mass, modified by stoping and resorption. The greater 



-'■'Knopf, op. cit., pp. 23-29 and PI. 1. 



so Geology and Ore Deposits of the Elkhorn Mining District, U. S. G. S. 22nd 

 Ann. Ept., Pt. II, p. 452. 

 si Loc. cit. 



