38 GEOLOGY OF ILLINOIS. 



two years ago, by some of the miners. It was eighteen or twenty 

 inches long 5 a siphnncle nearly three inches, in diameter projected 

 about four inches at one end ; the septa, somewhat loose, looked some- 

 what like a ribbed human body with a projecting neck. Of course, 

 those who saw it supposed that a petrified human trunk and neck had 

 been discovered. 



Trenton Limestone. This limestone is only met with in two localities 

 in the county. At Dunleith, and a little above it, there is a low outcrop 

 along the banks of the Mississippi river. It is here a light bluish-gray 

 rock, regularly and rather thinly bedded, with shaly partings, showing 

 many of its characteristic fossils. These layers are near the top of the 

 formation, and have some of the characteristics of the superincumbent 

 Galena. They, in fact, begin to partake of the nature of beds of pas- 

 sage into that rock. 



At Dubuque splendid specimens of Grajrfolitex have been found in the 

 Trenton ; also very finely preserved eyes of Trilobites. 



Other exposures of this limestone may be seen along the north branch 

 cf Fever river, commencing about three miles north-east of Galena, 

 and continuing until the Wisconsin line is reached. The outcrop attains 

 a thickness of about twenty-six feet at its heaviest exposure, at 

 Turtle's mill. It is made up of thin-bedded limestone, a rather thick- 

 bedded strata of glass rock, and grayish heavier bedded limestones. 

 Near the forks of Fever river, a cut of the Illinois Central Uailroad 

 shows a similar, but thinner section. Many of the well known fossils 

 of this formation are said to have been found at these outcrops. But 

 the conditions were not favorable for obtaining fossils at the time I 

 was there. 



This is the lowest formation anyAvhere outcropping in the county, or 

 that can be regarded as belonging to a section of JoDaviess county 

 rocks. We are now prepared to give that section, naming the approxi- 

 mate average thickness of the formations: 



Section of JoDaviess County Rocks. 



Quaternary Deposits. Alluvium, loess, river terraces, clays, sands ami hard-pan 20 to 75 feet. 



Niagara Limestone. Heavy-bedded reddish-brown dolomitic limestone, weathering into 

 cliffs and castellated exposures, similar m lithological character and appearance to the 

 Galena limestone 40 to 200 " 



Cincinnati Group. Green and blue and buff-colored shales ; thin-bedded gray limestone, 

 and hard, thick-bedded glassy rock 42 to 80 ' ' 



Galena Limestone. Heavy -bedded, cream-yellow dolomitic limestone, the lead rock of 

 the North-west ; somewhat gramilar, and crystaline, and showing beds of passage 

 into Trenton below 100 to 273 " 



Blue Limestone. Thin-bedded gray limestone and shales and glass rock of miners 10 to 26 " 



