192 Savage and Ross— *- Age of' Iron Ore. 



that the shiny character of the surface of the pebble-like con- 

 cretions in the iron ore bed is due to desert varnish, and 

 assumed that the material of the iron ore bed was transported 

 and deposited in dune-like masses by the winds under arid 

 conditions. The objections to this view are : (1) The iron ore 

 deposit is horizontal!}'' and regularly stratified, as may be seen 

 in figure 1, and shows none of the oblique bedding and irregu- 

 larities of stratification characteristic of wind deposition ; (2) 

 The shiny varnished appearance of the pebble-like concretions 

 is due to the iron, which is present not only as a film or rind 

 on the surface of the pebbles, but the larger part of the peb- 

 bles and also of the oolite spheres is composed of iron. The 

 surface of the oolite spheres has a varnished or shiny appear- 

 ance similar to that of the pebbles, and when some of the con- 

 centric laminae of the oolite grains are removed, the surface of 

 the inner ones are also seen to have a similar varnished appear- 

 ance. Concretionary pebbles of iron are found in many places 

 in a zone near the base of the Maquoketa shale, as at Scales 

 Mound, and Kingston, Illinois. The surface of these pebbles 

 in the lower part of the Maquoketa in Illinois has a shiny 

 appearance, similar to that of the pebbles in the iron ore 

 deposit in Wisconsin, yet the same layers in which they occur 

 also contain many shells of marine mollusks, as Ctenodenta 

 fecunda, C. obliqua, Cleidophorus neglecta and other species. 

 There seems no stronger reason for doubting the marine origin 

 of the original oolite in Eastern Wisconsin, the calcareous por- 

 tion of which has subsequently been replaced by the iron, than 

 for considering the lower fossiliferous part of the Maquoketa 

 at Scales Mound and Kingston, Illinois, in which similar iron 

 pebbles occur, as of nonmarine origin. 



The senior writer has shown that the lower part of the May- 

 ville limestone of Wisconsin, which immediately overlies the 

 bed of iron ore, corresponds in age to the Edgewood limestone 

 of Illinois and Missouri, which is much older than the Clinton 

 formation in the Appalachian region. Consequently, the iron 

 ore deposit can not be correlated with the Clinton of the east, 

 but is certainly older than the Edgewood formation. The evi- 

 dence indicates that it represents deposits iu local but appar- 

 ently connected basins (because of the marine fossils) during 

 late Maquoketa (Richmond) time, and after the main portion 

 of the normal marine Maquoketa sea had withdrawn from the 

 greater part of the region farther south in the Mississippi 

 Valley. 



The iron ore bed has been referred to by Chamberlin as 

 the " May ville ore bed," but he applied the name May ville* 



* T. C. Chamberlin : Geology of Wisconsin, vol. 2, p. 336, 1877. 



