GEOLOGICAL AND NATURAL HLSTORy SURVEYS. 187 



By " Tertiary clays " Mr. Hubbard understands what we now 

 designate "bowlder clay" or "till." They cov^er all the border 

 counties on the east and west slopes of the peninsula, and in some 

 cases stretch far inland. The Tertiary clays underlie the ancient 

 alluvions " t]n-ous:hout their whole extent. These are a formation 

 anterior to both the diluviums and alluvions, and are frequently 

 found extending far beyond the old lake ridge " (p. 122). 



Under the head of " Coal Measures " the " limestone stratum " is 

 so defined as to indicate its identity with the lower Carboniferous 

 limestone. He adopts Mr. Douglass's views respecting the existence 

 of " lower " and " upper " coal beds. The lower coal, he thinks, gives 

 promise of much usefulness. He recognizes it in Jackson. Ingham, 

 and Shiawassee counties, and says it is 3i to 4 feet thick near 

 Corunna. The accompanying shales extend as far east as Flint 

 River in Genesee County. " The coal of Shiawassee and Flint Rivers 

 appears to occupy the extreme edge of the coal basin" (p. 127). 

 The upper coal is recognized " as the northern part of Eaton County," 

 and probably underlies the whole of Clinton and Gratiot Counties. 

 In quality and thickness it is inferior to the lower coal. With the 

 " included sandstones " he associates the gritstones at Napoleon. 

 The " red or variegated sandstone " of Clinton and Ionia Counties 

 he thinks belongs between the upper and lower coals. 



The " subcarboniferous sandstones" are the same as heretofore 

 designated " fossiliferous, ferruginous sandstones," and are more 

 recently known as " Marshall sandstones," He anys " they make 

 their appearance at its eastern edge, on Lake Huron, near the en- 

 trance of Saginaw Bay." He seems to refer here to the Point au 

 Gres sandstone, which is a stratum in the lower Carboniferous lime- 

 stone. The " Point aux Barques sandstones," which are their real 

 equivalents, are treated under a separate head. 



The "clay and kidney-ironstone formation" is the upper and 

 larger portion of the "Huron group" of the writer [Winchell], and 

 lies undoubtedly in the horizon of the Chemung and Portage groups 

 of New York. 



The " sandstones of Point aux Barques," it is stated, stretch south- 

 westerly, along the swell of land which forms the summit level of 

 the Peninsula, into Hillsdale County, " where the green and yellow 

 fossili ferrous sandstones above described overlie them." But no 

 Kuch relation of superposition has been observed. Did it exist, the 

 "kidney iron formation" would be between, and this has a thick- 

 ness of several hundred feet. In fact, the " Point aux Barques sand- 

 stones " trend southwesterly and are in continuity with the sand- 

 stones of Hillsdale County. 



