of Burlington^ Iowa, and its Vicinity. 215 



No. 5 is a fine-grained sandstone, closely resembling 

 the upper part of No. 1, and in hand-specimens it would be 

 quite impossible to distinguish the difference. It is more 

 evenly bedded than No. 1, and generally harder, having 

 more carbonate of lime in its composition. It contains 

 an abundance of fossils, but wholly in the form of casts. 

 The cavities once occupied by the fossils are sometimes 

 found partially filled with pulverulent carbonate of mag- 

 nesia. 



No. 6 is a light gray, oolitic limestone, with fossils quite 

 plentifully and evenly disseminated through it, and vary- 

 ing but little in texture or color. In some places it is 

 thinly and regularly bedded, but in others it presents quite 

 a homogeneous aspect. The stone is of solid and good 

 appearance when taken from the quarry, but breaks into 

 small fragments upon exposure to the atmosphere and 

 frost. The fossils are not often well preserved in this 

 bed. Some of them have the appearance of having been 

 partially dissolved. The stone also adheres firmly to the 

 outer surfaces of them, and their cavities are frequently 

 filled with calcareous spar, which separates into its com- 

 ponent crystals, and destroys the fossil upon the first 

 attempt to remove it. Small masses of zinc blende are 

 also found here. 



No. 7 may be described as generally a light reddish, or 

 yellowish brown subcrystalline limestone, but is subject to 

 many changes in color, texture, and composition, both de- 

 pendent upon, and independent of, its stratification. For 

 convenience of description it may be divided into lower, 

 middle, and upper portions. 



The lower portion, from five to ten feet above No. 6, is 

 subject to fragmentary disintegration, and often leaves the 

 mass above projecting to a considerable distance, until 

 the weight becomes too great for its coherence to support, 

 when it is broken off in large masses, and rolls to the foot 

 to the bluff. 



