222 University of California Publications in Geology [Vol. 8 



portant ore bodies in situations where there is no suggestion of 

 magmatic emanations, I am inclined to the view that they may dis- 

 charge the same function even more efficiently as a consequence of 

 intrusion ; and I am, therefore, more impressed by the probability of 

 the first of these three possibilities than by that of the second. In 

 assuming the role of critic of the more popular explanation of ore 

 deposition I do not, of course, venture to hope that Professor Lindgren 

 will change his view as a result of my remarks ; but I shall be more 

 than content if I succeed in convincing the younger geological students 

 of this country that the origin of ore deposits in or near intrusives 

 is still an open question and that further observations, made in the 

 light of alternative hypotheses, are necessary before we can arrive at 

 a settled theory. 



LINDGREN 'S CRITICISM 



The Circulation of Ground-Water. — The phase of the question 

 which Lindgren deals with particularly is the origin of garnet zones 

 and associated ore deposits at the contact of intrusive rocks with lime- 

 stone. He says : ' ' These deposits are high temperature deposits. . . . 

 The lowest temperature at which garnets, diopside, etc., may form is 

 about 400° or 500° C. ... It devolves upon the supports of the view 

 set forth to explain the possibility of such a circulation upward along 

 the contact at temperatures of from 300° to 1000° C. The Daubree 

 experiment will really not suffice any more as an explanation." 



In reply to this I may say, first, that I have never invoked the 

 Daubree experiment to explain the upward circulation under the 

 conditions discussed, nor have I ever considered that the Daubree 

 experiment, the inferences drawn from it by various writers, or the 

 exposition of the fallacy of these inferences by Johnson and Adams 4 

 as in any way affecting the question at issue. The question is : Is it 

 possible for the ground-water of stratified rocks, assuming its presence, 

 to circulate upward in the heated zone peripheral to an intrusive mass, 

 or through the mass itself if the latter be rendered permeable by 

 fracture? I understand from Lindgren 's remarks just quoted thai 

 he considers this impossible, or at least that he is very skeptical as to 

 its possibility ; although he apparently regarded it as possible when he 

 wrote his monograph and folio 5 on the Clifton-Morenci district. If 

 he now denies the possibility of such upward circulation, it is easy to 



* Observations on the Daubree experiment and capillarity in relation to cer- 

 tain geologic speculations, Journ. Geol., vol. 22, pp. 1-15, 1913. 

 s Loc. cit. 



