McDONOUGH COUNTY. 257 



monostlgma, Stigmaria ficoides, 8. umbonata, Pinnulnria capillacea, Caul- 

 opteri* obtecta, C. acantophora, CarpoUthes multi-striatus. Owing to 

 the thiimess of the coal, the roof shales are removed in driving the 

 entries to the mines, thus affording a fine opportunity for collecting the 

 many beautiful fossil plants that they contain. The thickness of the 

 the coal at this locality varies from twenty-four to thirty inches, and 

 at the level of the prairie it lies from seventy-five to ninety feet below 

 the .surface. On all the branches west of Colchester the coal outcrops, 

 and is worked by tunneling into the hillsides. The city of Quincy, as 

 well as most of the small towns along the Chicago, Burlington and 

 Quincy railroad south of Bushuell, have for many years derived their 

 supplies of coal mainly from the Colchester mines. 



In the vicinity of Macomb the Colchester coal seam has not yet been 

 found of sufficient thickness to be worked. About a mile and a half 

 south-west of the town, a thin coal outcrops above the sandstone quar- 

 ries of Mr Stewart, which I am inclined to regard as the Colchester seam, 

 though it is here only about one foot in thickness. This may however 

 be an outcrop of the lower seam No. 1, but from the appearance of the 

 sandstone I believe it to be No. 2, thinned out here to about one-half its 

 usual thickness. In the vicinity of Colchester a very good sandstone is 

 found below the coal and from ten to fifteen feet in thickness. It is Xo. 

 11 of the foregoing section. This I believe to be the equivalent of the 

 sandstone at Stewart's, and the old McLean quarries near Macomb. A 

 section of the beds exposed in the vicinity of these quarries shows the 

 following succession of strata : 



Thin coal 1 foot. 



Slia'y clay 2 



Thin bedded sandstone .' 1 to 6 



il;issivt- sandstone 10 to 12 



Bituminous shale (coal Xo. 1 .') 4 



< "iii-lnmate of iron 



l-'ire-rlay J 



Bituminous slate or shales } 



Shale 5 



The horizon of coal No. 1 is here occupied by bituminous shales and 

 n six inch band of carbonate of iron. In the vicinity of Colchester, at 

 most of the outcrops we examined, the same horizon was represented by 

 dark -blue shales (Xo. 12 of the section previously given), containing 

 nodules of iron ore inclosing crystals of zinc blende. On the south-west 

 quarter of section 24, town 5 north, range 4 west, the following beds 

 were found exposed in connection with coal No. 1: 



Shaly sandstone 4 feet. 



Coal Xo. 1 2 " 



Fire-clay not exposed 



Shaly sandstone Ifi " 



St. Louis limestone C " 



34 



