PIKE COUNTY. 31 



considered in reference to the extent of surface over which it outcrops, or the 

 amount and value of the economical material which it affords. Although as a 

 building stone it is not quite equal to the magnesian beds of the Niagara group, 

 which outcrop in the vicinity of Pleasant Hill, it is, nevertheless, a very durable 

 stone, and may be made available for all the ordinary uses for which such a 

 material is required, and it is easily accessible over about one-half of the whole 

 area of the county. 



KeoJcuk Group. This group, which immediately succeeds the Burlington 

 limestone in the ascending order, outcrops over a considerable area in the north- 

 ern and northeastern parts of the county, where it is frequently found imme- 

 diately beneath the Coal Measures, the St. Louis group, which should properly 

 intervene, having been removed by denudation, anterior to the coal epoch. It 

 consists of light gray and bluish gray, cherty limestones at the base, which 

 closely resemble the upper beds of the Burlington limestone in their lithologi- 

 cal characters, so that it would sometimes be difficult to define the line of sepa- 

 ration between them, except for the fossils, which always serve to distinguish 

 them. Some of the limestone strata are quite as crinoidal in their structure as 

 the Burlington limestone, but they are usually more of a bluish gray in color, 

 and may therefore be readily distinguished, even in hand specimens, from the 

 underlying formation. There is usually a series of cherty beds, from ten to 

 thirty feet in thickness, separating the main limestones of these two groups, 

 which may properly be considered beds of passage from one limestone to the 

 other. The upper division of this group consists of calcareo-argillaceous shales 

 and thin bedded limestones, containing geodes lined with crystalized quartz, 

 chalcedony, calcite, dolomite and sometimes, but more rarely, with crystals of 

 zinc blende and iron pyrites, the latter usually in minute crystals implanted on 

 quartz. This division may be seen a mile and a-half southeast of Griggsville, 

 and, where it first appears beneath the Coal Measures which rest upon it here, 

 the geodes are found embedded in a ferruginous sandstone, that perhaps repre- 

 sents the conglomerate, which usually lies at the base of the Coal Measures. A 

 similar occurrence was observed at Moore's coal bank, in Scott county, as has 

 been mentioned in the report on that county. This indicates some erosive ac- 

 tion, anterior to or during the formation of this conglomerate, by which the 

 shales in which the geodes were originally embedded were swept away, and the 

 geodes were covered and enclosed in sand, which subsequently hardened into a 

 conglomerate. 



The shales and shaly limestones of the geodiferous division of this group, are 

 exposed in the vicinity of Perry Springs, and outcrop on the tributaries of 

 McGee's creek, in that vicinity. The springs flow out of these shaly limestones, 

 and probably derive the small amount of mineral matters which the waters con- 

 tain, from these beds. On McGee's creek, at Chambersburg, the limestones of 



