184 GEOTEKAL GEOLOGY. 



angle of dip has reached, in some places, twenty-eight 

 degrees with the horizon. 



This formation is entirely a Magnesian limestone with, in 

 some places, a considerable proportion of silicions matter in 

 the form of chert or coarse flint. A large part of it, especially 

 its lower portion, closely resembles both the Galena and 

 Lower Magnesian limestones, having the same want of 

 uniformity of texture and bedding, which causes it to weather 

 into rough and craggy forms upon its outcrops, and renders 

 it unsuited for purposes of architecture. 



Economic value. A large part of the formation, however, 

 is more evenly bedded, and taking it together it probably 

 affords the best and greatest amount of quarry rock of any 

 in the State. The quarries near Anamosa, in Jones county, 

 are most remarkable for the uniformity and precision of the 

 bedding of its strata. These quarries, together with those at 

 Le Claire and Farley, all of which are opened in strata of 

 Niagara limestone, will be found more particularly described 

 in another part of this report. Wherever this rock is 

 exposed there is always an abundance of material for roads 

 and for common masonry. 



At,Le Claire, most excellent common lime is prepared from 

 this formation, and a fair article of it may be made from 

 that of any part of it. Some of the layers, however, seem 

 much better adapted to the preparation of lime, although the 

 chemical analysis shows but slight difference of composition. 



4.— DEVONIAN SYSTEM. 



HAMILTON GK0TJP. 



HAMILTON LIMESTONE AND SHALES. 



Syn.— Upper, Heldeeberg Limestones in part of Hall, in Report op 

 Geology of Iowa, for 1858. 



Area and General Characters. The area of surface occupied 

 by the Hamilton limestone and shales, is fully as great as 

 those occupied by all the formations of both Lower and 



