DEKALB, KANE AND DUPAGE COUNTIES. 117 



however, including both exposures, and such intermediate beds as may be con- 

 cealed by surface deposits, cannot well exceed twenty-five or thirty feet. 



Continuing up stream, no outcrops or exposures of rock in place, are met 

 with, until entering the city of Aurora. Here, in the southern part of the city, 

 on the eastern bank of the river, at Hoyt's quarry, about forty feet of the 

 limestone is exposed. Of this, the upper nineteen or twenty feet is a rather 

 thin bedded buff limestone, with chert very abundant in layers and lenticular 

 nodules. The remainder of the excavation, below this, is in a regularly bedded 

 impure limestone, varying in color from light gray to buff or drab, and closely 

 resembling in appearance portions of the well known Joliet stone. The dip in 

 this quarry is to the northeast, and amounts to from one to four degrees. The 

 line of separation between the upper and lower beds is quite distinct in this 

 section. In the upper beds, a few indistinct fossils were observed : Atrypa 

 reticulariSj and Orthoceras undulatum, were the only species recognized. The 

 lower portion of the quarry, on the other hand, appeared to be entirely desti- 

 tute of fossils, but abounded in small geodes, containing crystallized quartz. 



In the northern part of the city, the limestone again appears on the western 

 bank of the river, at first, only at the edge of the water, but gradually appear- 

 ing higher on the bank, further up the stream. It also underlies the surface 

 farther up the bluffs, but how hi<rh cannot be exactly ascertained, as it is mostly 

 covered with soil. Nearly a mile above the city, there are several quarries on 

 the side of the bluffs, on the western bank of the river, which show vertical 

 cliffs of limestone from fifteen to twenty-five or thirty feet, or higher. The 

 stone in these quarries is an impure limestone, in some layers approaching a 

 true dolomite in composition, of a decidedly buff or yellow color. Some of the 

 beds, in some localities, are deeply stained with oxyd of iron, and present a 

 dark, reddish brown color. There was here, apparently, a slight local dip to 

 the westward, which, however, was not very noticeable. There may be, possi- 

 bly, a slight undulation of the strata, or anticlinal, having a strike about north- 

 west and southeast, but at all events, it is very inconsiderable, and does not 

 affect the general disposition of the strata in this region. I have considered 

 the rock exposed in these quarries, and along the river bank, as below the 

 cherty beds of Hoyt's quarry, and, perhaps the equivalent of the strata imme- 

 diately below them, though not exactly agreeing in lithological characters. I 

 have, however, no positive proof of this. But few fossils are to be found at 

 these localities ; the only specimens obtained were two or three imperfect Caly- 

 mene Blumenbachii, and the pygidium of an Illsens. 



To the north of these quarries, along the western bank of the river, and, 

 though to a somewhat less extent, on the eastern bank also, ledges of rock are 

 seen almost continuously, near the water's edge, for some seven miles, as far as 

 the town of Batavia. In most cases only a very limited thickness of the weath- 



