235 



" comes to nature too quickly," and is liable, therefore, to be 

 badly refined, breaking while hot under the tilt hammer, or 

 " brooming up " in the process of hammering. 



It is obvious that there is a loss in weight of iron in purchasing 

 the highly manganesian irons, but in those containing but little 

 manganese it is of no account, since it merely displaces a certain 

 proportion of carbon. It appears from the relative specific grav- 

 ities of the samples which I have analyzed, that a highly man- 

 ganesian iron may be readily known, its specific gravity being 

 less than that of ordinary white carboniferous iron. By a more 

 extensive series of researches much may be learned in relation 

 to the alloys of iron, and the importance of the business in a 

 practical view requires that such examinations should be made. 



Mr. Desor gave an account of the clay and drift deposits 

 in the vicinity of Lake Superior, and explained their con- 

 nection with similar deposits farther west. 



Along the rivers running into the Lake is a layer of«red clay 

 from forty to sixty feet thick, considered by some geologists as 

 tertiary, covered by a wide-spread drift deposit, which he consid- 

 ders as corresponding to the blue clay of Michigan. The blue color 

 being due to the decomposition of shells found in that locality. 

 On Mackinaw Island, at the height of two hundred feet, is a 

 deposit of red loam one hundred feet thick, also evidently cor- 

 responding to the red clay at the east end of Lake Superior. 

 The " yellow, hard pan," of the western geologists, Mr. Desor 

 considers a local form of the blue clay. 



The wide spread drift deposit of the West is particularly con- 

 spicuous in the rolling prairies. Boulders are sometimes found 

 on its surface, generally from ledges far to the north, some of 

 them having been brought six hundred miles. As they are as 

 large at their southernmost limit as at the north, the transporting 

 power can have lost none of its intensity. The drift is the 

 thickest near the Pictured Rocks, where it is three hundred and 

 forty-five feet thick. At Cape Girardeau, above the junction of 

 the Ohio and Mississippi Rivers, it is the thinnest. It extends 

 with scarcely an interruption from the Mississippi and the Lakes 

 to the Atlantic. From Zanesville, Ohio, to the Alleghanies, it is 

 wanting. On the eastern slope of the first branch of these 



