24 
STATE AGRICULTURAL SOCIETY. 
thickness varies from fifty to one-hundred feet. The product 
of its decomposition burns to a light buff or cream color and 
along the line of its exposure is used for making brick. The 
brick clay deposit in the neighborhood of Milwaukee is thought 
to be of this origin. 
The Clinton and Niagara Group , which comes next in order, 
consists of layers of limestone, beds of shale, (green, greyish- 
green, and arenaceous or sandy), and iron ore. As they occur 
along the eastern shore of Green Bay, these limestones are 
thin-bedded, compact dolomites, with thin shaly seams between. 
Near Sturgeon Bay they are quite white and are regarded as 
marble. But the most interesting member of this group is the 
stratum of Iron Ore which immediately underlies the limestone 
and rests upon shale. This ore occurs at several points through¬ 
out the district, but has not yet been discovered in large 
deposits, except in what is known as “ The Iron Ridge,” in 
Dodge County, which will be considered under its proper head. 
The extensive limestone formation which constitutes a broad 
belt of some thirty-six miles in width along the shore of Lake 
Michigan from the southern boundary to the extreme point of 
the peninsula between the lake and Green Bay, so nearly 
resembles the Clinton formation that they may with propriety 
be classed together as one group. Large areas of these lime¬ 
stone formations are obscured by extensive accumulations of 
drift; still there are numerous exposures, and in various parts 
of the district valuable quarries have been opened. The 
quarries at or near Racine, Burlington, Grafton, on Milwaukee 
River, Sheboygan, Ozaukee, Fond du Lac, and in Calumet 
County, are of this character. At Manitowoc it is so fine¬ 
grained, compact and uniform in crystallization, as to have 
taken the name of “marble.” The formation at Waukesha is 
so argillaceous in character, and so much less crystalline, with 
thin shaly partitions between the strata, that Mr. Lapham gave 
it the special name of Waukesha Limestone, to distinguish it 
from more coralline formations. 
Corniferous Limestone (“ shaly limestone,”) which is thought 
by Professor Hall to be identical with what is known in 
