422 INDEX TO THE STRATIGRAPHY OF NORTH AMERICA. 



Coldwater is the black shale which Lane refers to in the above quotation as the 

 equivalent of the Sunbury. The Coldwater comprises further the representative 

 of the Cuyahoga shale and possibly that of the Blackhand formation.''^" Lane cites 

 the following section from Huron County : 



Feet. 



Blue and sandy shales 172 



Light House Point conglomerate 4 



Blue shales with carbonate of iron, with Chonetes scitulus cf . pulchella common throughout. . . 720 

 Black shale (Sunbury), with Lingula melie and Orbieuloidea newberryi in Ohio 103 



1,000 ± 



The Coldwater shale thus represented and as originally defined covers the inter- 

 val between the Berea sandstone below and the Marshall formation above. Among 

 the subdivisions, the conglomerate in the above section is tentatively correlated by 

 Lane with the Blackhand of Ohio, and beneath it should come the representative of 

 the Cuyahoga shale. Lane gives a number of well sections showing variations in 

 color, composition, or thickness of the several subdivisions, and the strata have also 

 been described by earlier writers. 



The Coldwater shale is succeeded by the Marshall formation, into which it 

 passes by increasing sandiness without distinct plane of division. 



The Marshall formation as known in Huron County comprises, according to 

 Lane, °'^'* the following beds: 



Feet. 



Napoleon (Upper Marshall) sandstone 300 



Lower Marshall (original Marshall): 



Hardwood Point shales and sandy flags, f ossilif erous ( ' ' typical Marshall " fauna) 85 



Port Austin sandstone 23 



Sandy shale 68 



Point aux Barques sandstone 18 



Shales and flags with Romingerina julia 41 



Grindstones with bands of peanut conglomerate and broken goniatite shells 25 



560 



Lane comments: 



The facies with the battered shells, chip pebbles (now coal), Solens, and lamellibranchs is 

 a real shore facies. As we go toward the center of the basin the sandy facies of the Lower 

 Marshall seems to disappear, especially the clear white sandstone, nor is the upper sandstone 

 so thick. 



The Michigan formation, a sequence that carries brine and gypsum and is 

 of smaller extent, succeeds the Marshall. Lane regards it as the deposit of an 

 inclosed sea, like the Caspian. Its thickness is generally about 200 feet. At Mount 

 Pleasant, where it is thickest, the section is as f oUoavs : "^' 



Feet. 



Shale 5 



Sandstone 20 



Dolomite and shale ■ 75 



Anhydrite and dolomite 100 



Anhydrite 45 



Dolomite, shale, and anhydrite 103 



Sandstone 8 



Shale 5 



Sandstone 4 



Shale 15 



380 



