56 GEOLOGY OF ILLINOIS. 



The lower forty-eight feet of this section belongs to the Burlington limestone, 

 and furnishes most of the building stone, and limestone for the manufacture of 

 quick lime, to supply the city and adjacent country. The light gray limestones 

 are a nearly pure carbonate of lime in their composition, and often contain 

 pockets, lined with beautiful crystals of calcite. The buff and brown layers 

 contain carbonate of magnesia and iron in small quantities, and some of the 

 lower beds of this formation are highly magnesian, and approach a true dolo- 

 mite in their composition. On Mill creek, at the old mill, six miles southeast 

 of Quincy, there is about forty feet of this limestone exposed, the lower part 

 of which consists of alternating beds of light gray and brown limestone, all 

 of which are probably more or less magnesian in their composition, and afford 

 an excellent building stone, comparatively free from chert, and sufficiently 

 massive to furnish dimension stone of any desired size. From this point, to 

 the south line of the county, this limestone forms continuous outcrops along 

 the river bluffs, the exposures ranging from twenty-five to fifty feet or more in 

 thickness. This limestone outcrops only over a limited area in the southwest 

 part of the county, and a line drawn from the city of Quincy to the southeast 

 corner of township 3 south, range 7 west, would represent very nearly its 

 eastern boundary, while its western would be determined by the river bluffs. 

 The quarries at Quincy have afforded a good many fine examples of the fossils 

 peculiar to this group, among which the following are the most common spe- 

 cies : Spirifer plenus, S. Grimesi, Atliyris lamettosa. A. incrassatus, Chonetes 

 Illinoisensis, Productus semireticulatus, P. punctatus, Metoptoma umbella, Pla- 

 tyceras Quincy ensis, P. biserialis, Actinocrinus Verneuilianus, A. ohlatus, A. 

 Hageri, A. Christyi, A. pyriformis, Granatocrinm Norwoodi, and G. melo. 

 From the lower beds of this limestone, exposed in the river bluffs, between 

 Mill creek and the south line of the county, we obtained Actinocrinus carica, 

 a very rare species, not yet found at any other locality in the State, A. uni- 

 cornis, A. clarus, A. discoideusj A. verrucosus, Strotocrinus umbrosus, Codo- 

 naster stettiformis, and Pentremites elongatus, with three species of Plutycrinus 

 not yet determined. At Quincy, we obtained a number of specimens of the 

 remains of cartilaginous fishes, consisting of teeth and spines, and noticed 

 one layer of limestone, in the upper part of the quarries, that was well filled 

 with these fragmentary remains. The large spine, Physonemus gigas ) figured 

 on PI. II, was obtained from the quarries at Thayer's mill, about a mile 

 below the city. The " fish bed " of this division of the Lower Carboniferous 

 series was first noticed at Quincy, and a fine series of teeth and spines were 

 obtained from it as early as 1854. 



The fossil shells and crinoids above named, are nearly all of them peculiar 

 to this rock, and an acquaintance with them will enable the observer to dis- 

 tinguish this limestone from the Keokuk group, to which it is closely allied in 



