14 Natural History Bulletin. 



have furnished a very large proportion of the material used in 

 riprapping. At the upper end of the quarry coal-measure 

 shales and sandstones are seen resting unconformably on the 

 Devonian sandstones. The lower beds are very flexuous and 

 distorted. A well marked layer at any point may thin out 

 and disappear in a distance of twenty feet. The conglomerate 

 bed, number 6 on Robinson's Creek, is here well marked, the 

 fragmentary materials being interstratified with irregularly 

 contorted beds of shale and sandstone disposed at all imagin- 

 able angles and frequently thinning out within a few feet. At 

 one point observed in the face of the bluff the conglomerate 

 bed had a thickness of eight or ten feet, while only a short 

 distance to the left the same layer had thinned to eight or ten 

 inches. In the face of the bluffs at a height of about fifteen 

 feet, occurs a la3'er of impure coal about ten inches in thick- 

 ness, and above the coal are regular, horizontal, even-bedded 

 layers of sandstones representing number 8 on Robinson's 

 Creek. Below the coal seam all the strata are confused, 

 contorted, irregular; above the coal seam the layers are even, 

 regular and horizontal. 



There are two distinct sandstones belonging to different 

 ages, in the region about Pine Creek and Montpelier in Mus- 

 catine county, Iowa. One belongs to the Middle Devonian, 

 the other to the Lower Carboniferous. To avoid confusion I 

 have used at different times in this article the term Spin'/er- 

 bearing sandstone to denote the earlier of the two. We may 

 speak of them hereafter respectively as Devonian and Car- 

 boniferous sandstones. 



The Carboniferous sandstone is extensively developed 

 throughout the region from Buffalo to Muscatine. An ex- 

 posure of nearly a hundred feet in thickness may be seen at 

 Wild Cat Den, a mile and a half above Pine Creek Mills. At 

 Wyoming Hill, a short distance below^ Fairport, it is well ex- 

 posed and furnishes numerous remains of coal-measure plants. 

 In the lower part of the city of Muscatine it is again seen in 

 the high bluff, lying as usual above a layer of rather impure 



