PRELIMINARY CHAPTER. 15 



the following formations, in descending order: The Xiagara 

 Limestone, Cincinnati Group, Galena Limestone, Blue 

 Limestone. Buff Limestone, St. Peter's Sandstone, and the 

 upper surface of the Caleiferous Sandstone or Lower Mag- 

 ncsian Limestone. The Galena, Blue and Buff liinestom - 

 are now classed as divisions of the Trenton Limestone. 

 The Caleiferous sandstone can hardly be named among the 

 exposed and outcropping formations of Xorth-western Illi- 

 nois. It is the floor of Roek river, at a point where the 

 St. Peter's sandstone outcrops in high bluffs along the shores 

 of that stream. The local outcrops, superficial extent, 

 characteristic fos>ils. and weathered appearances and expo- 

 sures, are referred to in detail in the county reports, follow- 

 ing. In this place I shall simply speak of their general 

 characteristics and lithological appearance >. 



Tlic Xiayara Limestone. This is a heavily-bedded, dolo- 

 mitic. magnesiaii limestone, without any appearance of 

 slialey or arenaceous beds, so far as I have noticed. In 

 color, it ranges from a grayish-white to a brown or brown- 

 ish-red, often finely speckled with minute dendritic-looking 

 spots. In texture it is soft and fine-grained, like the Le- 

 clair limestone; tough, and of a horn-stone texture, like the 

 Cordova lime-burning quarries: crumbling, coarse-grained 

 and brecciated. like the quarries at Fulton City. And yet. 

 with all this diversity, there is a similarity of structure and 

 appearance, which makes it difficult to mistake the Xiagara 

 limestone for any of the other formations. From the north 

 part of Carroll county to Port Byron, in Rock Island 

 county, it caps the river bluffs, presenting that splendid 

 castellated brown-red appearance so familiar to travelers 

 on the Upper ^Mississippi river. It reaches a maximum 

 thickness of one hundred and seventy-five or two hundred 

 feet. It caps the mounds further north, and is called "the 

 Mound limestone" by PERCIVAL and other of the earlier 

 . geologists. By Dr. OWEX it was named the Corraline 

 and Pentamerus beds of the Upper Magnesian limestone," 



