5°° 



REGINALD A. DALY 



Weed and Pirsson 1 describe Judith Peak, Montana, as underlain 

 by a " stock" of porphyry. Their section of the "stock" shows, 

 however, a rapid constriction of the body as the section is followed 

 downward. As will be noted on a following page, the section of a 

 true stock typically enlarges downward so that such a body is "sub- 

 jacent" rather than "injected" with respect to the invaded forma- 

 tions. On the supposition that the section of Weed and Pirsson 



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 SCALE 



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Fig. 7 



correctly represents the actual underground relations, the Judith 

 Mountain body has its nearest relatives among "chonoliths" and not 

 among "stocks." 



Jaggar 2 describes the intrusive bodies of Dome Mountain and 

 Whitewood Canyon in the Black Hills as injected bodies of marked 

 irregularity both in shape and in relations to their respective country- 

 rock formations. These bodies seem to be transitional between 



1 Eighteenth Annual Report, U. S. Geological Survey, Part 3, 1898, p. 533. 



2 Op. cit., Plates 20 and 21, and pp. 209 and 217. 



