IOWA ACADEMY OF SCIENCES. 99 



SIGNIFICANCE OF THE OCCURRENCE OF MINUTE 

 QUANTITIES OF METALLIFEROUS MIN- 

 ERALS IN ROCKS. 



BY CHARLES R. KEYES. 



The present consideration of the occurrence of many of 

 the more common metals in minute quantities in the rocks 

 had its foundation in an inquiry started by Messrs. Wins- 

 low and Roberson, in connection with the investigation of 

 the Lead and Zinc deposits in Missouri, undertaken by the 

 geological survey of that state. Although the work of 

 these authors ended with their general report, the special 

 phases of the investigation were not dropped by the sur- 

 vey. While the later results are by no means complete as 

 yet, owang at that time to circumstances entirely beycmd 

 the control of the scientific corps of the organization, it is 

 believed that there were some points reached in sufficient 

 detail to make a general statement worthy of representa- 

 tion in synoptic form. 



The lead and zinc deposits of southern Missouri and the 

 contiguous parts of the adjoining states are of more than 

 ordinary interest at this time, for the reason that they pre- 

 sent, in an exceptionally fine way, many of the most 

 instructive phases of ore-genesis. 



The recent discussions on the ore deposits by the geolo- 

 gists have awakened a new interest in the whole subject, 

 and clearly indicate that the time is opportune to begin 

 the consideration of systematic plans of inquiry, to devise 

 special methods of work, and to formulate critical criteria 

 which will enable all investigations to be brought to a sat- 

 isfactory basis for comparison. 



The observations herein recorded are offered chiefly in 

 criticism of certain methods of inquiry which are com- 



