494 HISTORICAL GEOLOGY. 



Lake Ontario. East of the Hudson it occurs over large areas as part of the Taconic 

 series described beyond. In the west-central j)ortiun of southern New York it is covered 

 to a depth of 2000' or more by later formations. 



The Utica shale is 15' to 35' thick at Glen's Falls, in New York ; 250' in Montgomery 

 County ; 300' in Lewis County. 



The Hudson River shales cover the region north of Lake Champlain, in Canada, 

 reaching to Quebec, and northeastward to Montmorency and beyond. They also cover 

 a small area near the center of the Trenton limestone region of the Ottawa basin. ' In New 

 York they include shales and sandstones. They are the Lorraine shales of Jefferson 

 County (the Pulaski shales of the New York Annual Reports), containing some thin beds 

 of limestone. The thickness of the shales, in Schoharie County, N.Y., is 700' ; in western 

 Canada, 700' ; in a boring at Utica, N.Y., 90', below 710' of Utica shale. 



In Pennsylvania the Hudson shales (Matinal of Rogers, or his No. Ill) border the 

 Trenton areas, and have in general great thickness. 



In Ohio the Trenton, in the Cincinnati region, lies beneath 700' or so of beds of impure 

 thin-bedded limestone and shale of the Hudson (Cincinnati) epoch ; and to the north these 

 shales are 500' to 1000' thick, and include at base 300' of Utica shales. The same beds 

 are continued westward into Indiana, in the eastern part of which State the thickness is 

 about 1650'. Of this, 500' to 600' are Trenton and Galena limestone ; it is usually of gray 

 to buff and white color, but in the northwestern part of the state, chocolate-brown. 



South of the Ohio, in middle Kentucky, the Trenton, which includes the "Blue lime- 

 stone" of Owen, is well represented by thick-bedded limestone, with some shaly seams; 

 the beds have a small northward dip, toward the Cincinnati region and Lake Erie, along 

 the area of the " Cincinnati anticlme." 



In the valley of east Tennessee, the Trenton includes the "Blue or Maclurea limestone " 

 of Safford, and is 200' to 600' thick ; and above this comes the " Nashville shale " of the 

 Hudson epoch, which is partly calcareous (becoming increasingly so to the westward) and 

 is about 2000' thick. In the Maclurea limestone occurs, as an interpolated bed, the clouded 

 red limestone, affording the famous Tennessee marble ; it is about 380' thick. In middle 

 Tennessee the Trenton and Nashville strata are horizontal, and all is limestone, the later 

 less pure ; thickness about 450'. (Safford.) 



The Galena or lead-bearing limestone, of Wisconsin and the adjoining States in the 

 West, is 100' to 200' thick in northern Illinois and about 250' thick near Dubuque, Iowa ; 

 and the underlying Trenton 20' to 100'. 



In Wisconsin and the adjoining part of Minnesota the Trenton limestone is 300' to 

 350' thick ; the lower thinner part represents the Birdseye and Black River limestones of 

 New York. The upper part is the Galena limestone. Although mostly a dolomyte, it 

 is not all so ; in some parts of the lead region only the lower 18' to 25', called the Buff 

 limestone, out of a thickness of 100' or more, is magnesian. The Buff limestone from the 

 southern part of the town of Bristol afforded calcium carbonate 56-07 to magnesium car- 

 bonate 35-32. An associated blue limestone afforded 84*02 of the former to 5-33 of the 

 latter ; the rock of another bed, 97-92 of the former to 1-00 of the latter. (J. D. Whitney, 

 T. C. Chamberlin.) 



In Iowa, at Washington, a boring struck Hudson shales at 700', the Galena limestone 

 at 800', the Trenton at 1020', and St. Peter's sandstone at 1100' ; and below this, at 1230', 

 the magnesian limestone. 



In Minnesota, the Trenton, as it occurs near Minneapolis, consists of dolomitic lime- 

 stone, more or less argillaceous, of a buff to a drab color, with intercalated shaly portions 

 and blue shale at base. The thickness in the State is 15' to 70'. The Trenton in Missouri, 

 according to Broadhead, has a probable thickness of 400'. 



r. In the Bncky Mountain region. — The Calciferous period is represented probably by 

 the Ute limestone in the Wasatch, 1000' to 2000' thick ; it includes beds in the House 



