14 NOTES ON THE NORTHWEST. 



mentioned, will present a wide and fertile field of discovery 

 to any geologist whose good luck it may be to give it a 

 thorough exploration. For there he will find an opportunity 

 not only of studying the continuation of the secondary 

 cretaceous formation previously described, but likewise of 

 discovering the approach to a tertiary formation ; the equiva- 

 lents of which are doubtless to be found to the west of the 

 Rocky Mountains, as they have already been to the east, on 

 the Atlantic borders." 



This country is probably one of the most remarkable on 

 the earth, for the variety and abundance of its mineral de- 

 posits, and especially for those which are of most extensive 

 use in the arts. The sulphuret of lead occupies about one 

 degree of latitude, extending north from a point on the Mis- 

 sisippi, some eight miles below Galena, and lying on both 

 sides, varying in width till it covers as great an extent from 

 east to west. On the east side of the river the mineral is 

 found principally in a clay matrix, at a depth of sometimes 

 only five or six feet from the surface ; on the west side of 

 the river it nms at the depth of one hundred feet or more, 

 overlaid with magnesian limestone. To the south-west of 

 the lead deposit is a very abundant bed of iron, extending 

 from the Maquoqueta River south and west to the Wabesepi- 

 nicon, in the counties of Jackson and Clinton, in Iowa. The 

 extent of this mineral deposit is not known, but is proba- 

 bly forty miles or more northeast and southwest, with a 

 breadth not less than twenty or thirty miles. The copper 

 region extends north from the lead deposits to Lake Superior. 

 Its precise limits are not known, but it embraces about 

 300 miles square ; it is found south of latitude 43°, 

 in large quantities, and beyond 47° north. From east to 

 west it has an equal extent, being found in situ on Blue 

 Earth river, west of the Missisippi, in 94"^, and east as far as 



