STEPHENSOX COUNTY. 69 



fully, but shall briefly give the superficial boundaries and area, as marked 

 upon our map of this region. 



All that part of the county between the Pecatonica river and Yellow 

 creek, except a small strip east and south of Winslow, and except the 

 development of the Cincinnati group at Waddam's Grove, Xew Dub- 

 lin, Kent, and along the banks of the Yellow creek, is underlaid by the 

 Galena rocks. All that part of the county north and east of the Peca- 

 tonica river, except a strip in the bed of and along either side of Eock 

 run, is underlaid by the same. The south-eastern part of the county, 

 nearly up to the Pecatonica river, and nearly to the track of the Illinois 

 Central Kailroad, with the exception of a strip along the south-eastern 

 corner, and a few isolated patches in the eastern part of the township of 

 Silver Creek, is also underlaid by these same rocks. 



Fossils. Few fossils are found in the Galena limestone in Stephenson 

 county. The characteristic EeceptacuUtes sttlcata, called by the miners 

 and quarryinen " lead blossom," and " sunflower coral," is found at 

 Freeport and Cedarville in great abundance, but good specimens are 

 hard to obtain, on account of the friable nature of the stone in which it 

 is found. At the former place, a specimen of Receptaculites orbicularly 

 was noticed. Two or three species of Murchisonia, fragments of several 

 species of Orthocera, one or two well known Orthis, two species of 

 Pleurotomaria, a small Bellerophon, and a rather well defined Ambo- 

 nycliia, were the fossils most usually observed. They all exist in the 

 form of casts, and perfect cabinet specimens are hard to find. 



The Blue Limestone. This, the middle division of the Trenton, is of 

 limited extent in this county. Of course, in many places marked on the 

 map with the color indicating the Galena, a shaft sunk down a short 

 distance would strike the Blue limestone ; but we now describe it as 

 the surface rock, and only speak of it, where developed, as a surface 

 rock. Kock run cuts into the Blue limestone soon after entering the 

 county, and all along its banks, on both sides, until within a mile or two 

 of its confluence with the Pecatonica, this rock outcrops and shows 

 itself. Some of the high, rocky banks are overcapped with the Galena, 

 but the usual rook is the Blue. At the railroad bridge of the Western 

 Union Railroad Company, over Rock run, the railroad track is about six 

 feet below the junction of the Galena and Blue. Stepping west, out of 

 the railroad cut, there is a perpendicular descent of thirty-three feet, 

 from the track down to the water level, making the whole thickness of 

 the Blue, at this place, about thirty-nine feet. The lower part of this 

 outcrop is very blue, the upper part yellowish, with thin strata, and 

 gradually changing in lithological character, until the overlying Galena 

 just east of the bridge, is reached. This is a very interesting section. 

 One and a half miles below this locality is another quarry, opened in 



