REVIEWS 565 



The ore has a bedded structure. The author beHeves it 

 was originally a deposit of ferric hydrate or limonite formed in comparatively 

 stagnant shallow water under conditions similar to those conditions existing 

 where bog or lake ores are being formed today, and that through subsequent 

 changes, long after the iron was deposited as limonite, while the formation was 

 deeply buried below the surface and subjected to heat and pressure, the original 

 limonite became to a large extent dehydrated and changed to hematite. 



The extent of the ore is undetermined, but is in places 35 feet thick at 

 right angles to the bedding. 



One point in connection with the later formations of the region may be 

 noted. The St. Peters sandstone is said to be unconformable on the Lower 

 Magnesian limestone. This is also true in some other parts of the state, 

 and perhaps generally, and gives point to the inquiry as to whether the 

 Lower Magnesian limestone should not be classed with the Cambrian, rather 

 than with the Ordovician, making the unconformity the plane of division 

 between these two systems. This is the classification which was sug- 

 gested by the Geological Survey of Wisconsin in 1881 (Vol. I). 



R. D. S. 



