146 GEOLOGY OF ILLINOIS. 



their action Lere. In the spring of the year the ice in Rock river some- 

 times, impelled by the strong current, gorges, until it rises to the hight 

 of fifteen or twenty feet, and then with a cracking roar it tears rocks 

 from their beds and .trees from its banks, grinds them in its strong jaws, 

 and throws them high on the land or strews them along its bottom. 

 But away from the river the clays of the drift appear as if deposited 

 and arranged in peaceful waters. 



The Carboniferous System. While making examinations at Sterling, 

 I was repeatedly told that coal had been found three or four miles be- 

 low the town. The supposed outcrop was stated to be a thin seam in a 

 bend of the river, not far from the edge of the water. The same state- 

 ment is made, I think, in Dr. J. G. NORWOOD'S small report upon the 

 coal-fields of Illinois. I sought out the locality, examined the river, and 

 made inquiries of an intelligent farmer, who has resided near the spot 

 for many years. With him the existence of coal in the neighborhood 

 was a faint tradition, nineteen or twenty years old. An examination of 

 the river showed that its bed or floor consisted of the sofr, white, den- 

 drite-speckled upper division of the Niagara limestone. Gravelly banks 

 of river drift rose on one side some twenty-five feet from the water's 

 edge ; a low alluvial bottom lay between the river and the high prairie 

 on the other. No sign of any ontcr6pping rock exists, except in the 

 bed of the river. This is the general character of Hock river from 

 Sterling to about seven miles below Erie. No coal seam or outcrop of 

 coal, in my judgment, exists at the point designated. Some one, digging 

 along the banks of the stream at an early day, doubtless came upon a 

 small deposit of float or drift coal. Tradition has kept the circumstance 

 alive, and it grows with the passing years. 



The edge of the Coal Measures, however, extends thinly into White- 

 side county, at its south-western corner. Opposite Erie, the south bank 

 of Eock river begins to assume the character of a low bluff-line. In 

 descending the stream these bluffs rise in altitude, become more abrupt 

 and broken; and such are their general characters until the Mississippi 

 range of bluff* is reached, several miles below Eock Island. For most 

 of the distance the glancing waters of Eock river hug their bases. On 

 the north side of the stream the low alluvial bottom spreads out, widen- 

 ing in proportion as the range of hills rise in hight. A hundred feet is 

 perhaps the highest altitude attained by these^ bluffs. A short distance 

 below the western line of the county, coal begins to outcrop in the sides 

 of these bluffs. Still lower down, at Aldrich's coal mine, the seam is 

 some four feet thick, and is extensively worked. Cannel coal, soap- 

 stone, fire-clay, black-slate, and a stratum of black limestone are asso- 

 ciated with the coal. The outcrop is in the side of the hill, at a consider- 

 able elevation above the waters of Eock river. Below this mine, and in 



