204 GEISTEBAL GEOLOGY. 



shown in the next preceding full page sketch, which also 

 shows an exposure of a part of the Kinderhook beds, the 

 projecting portion being Burlington limestone. The locality 

 is near " Starr's mill," about three miles northwest from 

 Burlington. 



The lower division of this formation is composed of 

 yellowish, gray subcrystaline limestone, about twenty -five feet 

 in thickness. It is somewhat regularly bedded and seldom 

 has any shaly or clayey matter in the partings of the layers. 

 A few feet in thickness of the lower portion, where it joins 

 the Kinderhook beds, are sometimes a little sandy, but 

 rarely so. 



The central portion contains the purest and best limestone 

 layers, but they gradually become flinty towards the top as 

 they merge into the silicious beds of passage to the upper 

 division. 



These last named beds are composed of compact cherty or 

 flinty layers alternating with thicker beds of looser silicious 

 but not sandy shales, of a light yellowish color, and an 

 occasional thin, irregular layer of limestone. These silicious 

 beds are also about twenty -five feet in aggregate thickness, 

 making fifty feet for the whole thickness of the lower division. 



The upper division consists in its lower portion of light 

 gray subcrystaline limestone, the color, however, varying to 

 yellowish gray, and is about fifty feet in thickness. It is 

 composed of somewhat regular layers, usually thin, but 

 sometimes massive, with occasional clayey partings, but the 

 latter are not common. The limestone of this division is, as 

 a rule, more silicious than that of the lower division. Even 

 those layers that are not intercalated with flinty seams have 

 numerous small flinty masses imbedded in them, and the 

 fossil shells they contain are not unfrequently silicified when 

 the rock imbedding them is not so. Towards the top the 

 silicious matter increases in amount, until the limestone 

 merges into the silicious beds which complete the formation 

 and form a final passage to the Keokuk limestone. In the 

 vicinity of Burlington these silicious beds are not found to 



