268 SPARKS FROM A GEOLOGIST'S HAMMER. 



Grand Rapids on the west, and on the shores of Saginaw 

 Bay on the east, and undei'lies Washtenaw and Jackson 

 counties on the south. Next, in descending order, comes 

 the Marshall Group, consisting chiefly of sandstones whose 

 outcrops create the most elevated and hilly belt of the 

 whole peninsula. The other formations follow downward 

 as shown in the following table: 



( 1. Woodville Sandstone. 



I. Upper Carboniferous. - 2. Coal Measures proper. 



(3. Parma Sandstone ("Conglomerate"). 

 1. Carboniferous Limestone. 



II. Lower Carboniferous^ 2 - Michigan Salt Group. 



( (a) Napoleon Sandstone. 

 Marshall Group. ] (6) Red Shale 



I (c) Marshall Sandstone. 



1. Huron Group... \ <> J?' 4 ? 80 1 Chemnn S' 



III. Devonian 1 ^ 6 > Black Shale <" Genesee "> 



2. Hamilton Group. 



.3. Corniferous Limestone. 



( 1. Lower Helderberg or Water Limestone. 



IV. Upper Silurian -j 2. Salina Group. 



( 3. Niagara Limestone. 



This definite exhibit of the geological succession in the 

 lower peninsula had never been made before. The Car- 

 boniferous Limestone had never before been identified in 

 the state, but had been generally confounded with the 

 Monroe and Mackinac limestones. The Michigan Salt 

 Group was a totally new and previously unsuspected 

 formation. It is repeated in no other state in the Union, 

 and is known elsewhere only in New Brunswick, Nova 

 Scotfa and Cape Breton, where later researches have shown 

 it to possess a still greater development. The fact that 

 the formation underlies all the central part of the state 

 was not only unsuspected, but was a fact out of harmony 

 with the theory then prevailing respecting the origin of 

 gypseous deposits. Geologists generally had held gypsum 



