170 KEMP'S ORE DEPOSITS. 



brings them up from below. Haworth discusses a possible pre- 

 cipitation from the ocean, as is outlined under Example 24, and 

 Clerc mentions the pockets of slate and coal as a probable source. 

 Further and more extended study of the mines has been much 

 needed. 



A brief outline of Dr. Janney's views is here given, which has 

 been abstracted from manuscript that he has kindly allowed the 

 writer to see in advance of its publication. In the forthcoming 

 report all the lead or lead arid zinc regions of the Mississippi 

 Valley are considered together. They are described as occurring 

 along three lines of upheaval. The region of Wisconsin and Iowa 

 is on the flanks of the Archaean " Wisconsin Island " of Chamber- 

 lain, referred to above under 2.06.01. The southeast and southwest 

 Missouri regions are on the Ozark uplift, while a minor argentif- 

 erous galena district is on the line of the Ouachita uplift of Ar- 

 kansas and Indian Territory. The formation of the ore bodies in 

 the first three of these is regarded as having been in general the 

 same. They are thought to have originated from uprising solu- 

 tions, which came through certain principal fissures, and spread 

 laterally into strata favorable to precipitation. In southwest Mis- 

 souri this was the Cherokee limestone of the Lower Carboniferous. 

 In its unaltered state it is an extremely pure carbonate of lime. It 

 has a maximum thickness, where not eroded, of 165 to 200 feet, 

 and contains many interbedded layers of chert. Much organic 

 matter, and more or less bitumen, are also at times present. The 

 limestone seems to have been raised above the ocean level at the 

 close of the Lower Carboniferous and to have remained for a long 

 period exposed to the atmospheric agents. Much caving in of 

 unsupported layers of chert and much attendant brecciation re- 

 sulted. The general stratum became quite open and cellular in 

 certain portions. At a later period, supposed from several indica- 

 tions to be at the close of the Cretaceous, dynamic disturbance 

 occurred, which along certain lines produced fissures, sometimes 

 parallel, sometimes intersecting. Solutions arose through these 

 which dolomitized much of the remaining limestone and caused 

 additional porosity. Zinc and lead ores were afforded, and where 

 the conditions were favorable they spread laterally from the fis- 

 sures and deposited the sulphides in the cellular rock or replaced 

 the limestone itself. The intersection of crossing fissures is a fre- 

 quent point of deposition, and at times parallel master fissures 

 have given a wide area of impregnation. This form of ore fa- 



