1884.] 203 [Wadsworth. 



or molecular transference — a transference of material, leading to 

 the segregation or localization of the ores in the places in which 

 they are now found ; it manifests itself in the deposition of min- 

 eral matter in the veins and cavities of the rocks themselves, in 

 deposits from springs, in bogs, lakes, etc. From this it would fol- 

 low that all ore deposits, not eruptive, are superficial phenomena 

 as regards the earth, and dependent on its external agencies ; 

 although they may be deep enough so far as man is concerned. 

 Again, few of these ore deposits would be expected except in 

 regions in which percolating waters and their resulting meta- 

 morphism have been efficient agents j 1 while the various forms of 

 ore deposits would be expected to be associated with, and grade 

 into, one another. 



APPENDIX. 



It has been thought that the writer's meaning in the above pa- 

 per would be better understood, if some illustrations were added 

 to show how the principles employed have been varied by him to 

 accord with the special conditions observed in different localities. 



Heidelberg, Feb. 14, 1885. 



COPPER DEPOSITS. 



In the famous districts of Portage Lake and Keweenaw Point, 

 south of Lake Superior, the rocks consist of a mixed series of 

 old basaltic lava flows and conglomerates traversed in part by 

 fissure veins. 



Locally the conditions in which the native copper is found in 

 these districts give rise to four forms of deposits, known as : 



1. Amygdaloid Mines in which some of the thinner lava flows 

 (melaphyrs) are worked, the copper being distributed through 

 them in an irregular manner. 



2. Ash-bed Mines which are in reality the same as the Amygda- 

 loid but in the "Ash-bed" the melaphyr is of a more irregular, 

 open, and scoriaceous character. 



3. Conglomerate Mines in which old sea-beach conglomerates 

 are mined. 



4. Vein Mines in which true fissure veins are worked. 



All these deposits seem to the writer to have been produced by 



1 Whitney. Contributions to American Geology, 1880, Vol. I. The Auriferous 

 Gravels of the Sierra Nevada of California, pp. 310, 331, 350, 35G. 



