WITH THOSE OF NEW YORK. 287 



of limestone twenty-five feet thick, with about four feet of shale 

 below ; the limestone at this point has lost the sandy and impure 

 character which it has further east, and assimilates more with the 

 lower part of the Niagara limestone. The only fossil met with 

 in this mass on the Niagara river, was the DeUhyris radiatns, 

 which is found extending through the shale above, and in the 

 lower part of the limestone. 



In crossing the country from Galena to Chicago, few opportu- 

 nities oHered of examining the strata except at detached points. 

 The only rocks seen on the direct route are the two limestone for- 

 mations, the lower including Niagara and Helderberg, and the 

 upper the carboniferous ; and, from the great extent of level coun- 

 try, I was unable to see the intervening rocks. 



I had an opportunity of examining the rocks on the northern 

 and northeastern shores of the southern peninsula of Michigan, 

 but my observations were loo cursory to admit of any thing like 

 a connected view of them. The limestones of the Helderberg 

 series, principally the corniferous and Onondaga masses, form 

 the rocks of many of the bays and harbors ; characteristic fossils 

 of these masses being recognizable in those examined. At 

 Mackinak, the upper part of the Onondaga salt group, and pos- 

 sibly a small portion of the water-lime gi'oup, form all the rocks 

 seen. The former is partially altered from its usual characters in 

 New York, some parts exhibiting large angular cavities, the whole 

 appearance being that of a vesicular mass ; and had the cavities 

 been spherical instead of angular, it would have been referred 

 to igneous origin. This mass being isolated, renders it difficult 

 to trace its connection with those appearing to the south and east 

 of it; but from its great similarity to the salt group of New 

 York, and from its apparently passing beneath those representing 

 the Helderberg series, no doubt remains as to the propriety of 

 this reference. 



The exhibition of strata along the line of the section given, 

 illustrates some very interesting points in the geology of our coun- 

 try, and proves the existence and order of succession in certain 

 rocks, and their equivalents over wide areas ; offering us facts 

 which will still further enable us to solve the problem of the con- 



