WHITESIDE COUNTY. 149 



have worn it down and carried it away, until nothing but small patches 

 and basins remain. 



Its place in the strata of Illinois rocks is at the base of the Coal 

 Measures. It belongs. 1 think, to the Millstone grit, which, in the West, 

 is often only a tine-grained, arenaceous rock ; but in other localities, is 

 made up of coarse sandstones, pebbly conglomerates, and grits. 



j;,.vs/7.v. The Unionville quarry has afforded a considerable number 

 of impressions and casts of fossil plants. The most conspicuous among 

 these is a Calamite. the ('ulfimites camueformis, I think. The casts of 

 this plant are from one and a half to four inches in diameter, the 

 joints from three to about eight inches in length, the surface finely 

 marked with longitudinal lines. The friable nature of the rock makes 

 it difficult to obtain specimens. A species of Lepidodendron has also 

 left some well-defined impression. It seems to have been as thick as a 

 man's arm, and the impressions have a rough, shark-skin, rattlesnake- 

 like appearance. I could not obtain a good specimen, and am unable to 

 give it-< specific name. Some other sections of what appeared tolje a 

 plant, were observed : but the impressions were too indefinite for iden- 

 tification. 



The y'uujara I,ime*tone. A large extent of this county is underlaid 

 by this formation. Probably all that part of the county south of Eock 

 river is underlaid by the Niagara, except a little strip along the Ster- 

 ling dam, and the carboniferous bluffs below Prophetstown. In all this 

 extent of territory there is not an outcrop or quarry, however, of any 

 kind, except those in and along the bank of Eock river. The surface is 

 low. and the underlying rock runs low. The river, from Sterling to its 

 exit out of the county, every few miles, runs over rocky beds of porous, 

 dendrite-specked. yellow Niagara limestone. Just below the dam at 

 Sterling, at Lyndon, at Erie, seven miles below Erie, and at many other 

 intermediate localities, quarries are opened at the water's edge, or in the 

 floor of the river ; and. judging from the appearance of the low wet 

 prairies south of the river,, the Niagara runs back nearly level, perhaps, 

 beyond the southern limits of the county, before running under the Bu- 

 reau and Henry county Coal Measures. 



About a mile above Sterling, on the north bank of the river, a series 

 of Niagara quarries are extensively worked. The formation here is 

 worked down about thirt\ -five feet, and the rock is full of chert bands, 

 and is speckled with dendrite markings. The layers, although thin- 

 bedded, are so uncouth and rough that no mason could build them into 

 a handsome wall. The bottom layers are of a dull green color, and 

 soon pass into the underlying Cincinnati shales. 



