118 GEOLOGY OF ILLINOIS. 



ered edges of the strata are to be seen ; at none of the intermediate points is 

 there to be seen a good section, where either of the beds observed in the south- 

 ern exposure at Aurora, can be recognized. The strata generally lie nearly 

 level, though there are, in some places, appearances of local dipping, which may 

 perhaps be sometimes due to the undermining and consequent tumbling of large 

 masses of the rock. About two miles and a-half north of Aurora, a cherty 

 band may be traced in the rock for a short distance, and then disappears. It, or 

 another similar one, again appears at the base of the bluff near the mouth of 

 Mill creek, about a mile and a-half below Batavia. For nearly half a mile, the 

 limestone appears on the banks of the creek also. It is here a brittle, yellow 

 limestone, thin bedded, and quite fossiliferous in places. One of the best expo- 

 sures of this rock is on Mr. Stevens' place, at the old milldam, a few rods above 

 the crossing of the wagon road from Aurora to Batavia. Here some layers are 

 almost entirely made up of casts of Pentamerus oblongus, with very rarely a co- 

 ral or other fossils. 



Between this point and Batavia, although the ledges still continue along the 

 base of the bluffs, there is but one exposure of more than a very few feet ; a 

 disused quarry, about a mile south of the latter place, which shows a perpen- 

 dicular cliff of about twenty or twenty-five feet, all apparently of one bed of 

 yellow or buff limestone. No fossils were afforded by this locality. 



At Batavia, in the quarries on both sides of the river, the beds are precisely 

 similar to and probably identical with those worked at Hoyt's quarry in Aurora. 

 In Mr. Barker's quarry, on the western side of the river, there is about twenty- 

 five feet of buff and drab limestone, overlaid by eight feet of the upper cherty 

 layers ; the line of division between the two is very distinct. -This upper 

 cherty portion of the rock appears in the exposure to be much shattered, but is 

 consolidated again by a stalagmitic cement. It is altogether worthless as a 

 quarry rock, and is very troublesome to remove. Throughout the greater part 

 of the quarry, the strata lie horizontally, but at its northern end there is a sud- 

 den dip to the southward of from ten to fifteen degrees, bringing the lower beds 

 to the level of the top of the quarry. On the opposite side of the river, the 

 same dip is to be seen in Shannon's quarry, exactly where the strike would lead 

 us to look for it. In the three principal quarries on the eastern side of the 

 river, those of Messrs. Starkey, Shannon and Randall, respectively, the same 

 lower beds are shown as at the one already mentioned on the western bank, but 

 at Shannon's quarries only, are the upper cherty beds exposed. Near the bot- 

 tom of this quarry there is also a thin stratum of bluish shaly limestone, and 

 a seam, two or three inches thick, of sandstone, which is probably only local. 

 A very noticeable feature in all of these quarries, is the presence of large, well 

 defined, perpendicular joints, trending about E. S. E. and W. N. W. Another 

 set of joints, at right angles to these, is less conspicuous. In Shannon's 



