172 GEOLOGY OF ILLINOIS. 



beds of heavy coarse gravel were observed. The regular drift deposits 

 of the county belong to the lower and older drift clays. I could observe 

 nothing like glacial action, and the only evidences of the ice forces are 

 the boulders dropped from the icebergs floating over the submerged 

 prairies. 



Coal Measures. 



On all the old geological maps of the State which I have seen, the nor- 

 thern line of the Illinois coal field is marked too far south, both in this 

 county and in Henry. According to these maps, about one-half of this 

 county the north half is underlaid by Silurian rocks. The north boun- 

 dary line of the Illinois coal field should commence at a point in the east 

 line of Bureau county, ten miles south of the north-east corner of the 

 county, nearly due west of Homer Station, on the Illinois Central Eailroad. 

 Thence it should be drawn nearly due west, but curving or bellying a little 

 to the south, until it crosses the track of the Chicago, Burlington and 

 Quiucy Eailroad, a little south-west of the village of Maiden ; thence it 

 should bear off a little north of west until it intersects Green riv( r at the 

 north-east corner of the township of Gold ; thence down Green river to a 

 point north of Geneseo, in Henry county ; thence north-west until Eock 

 river is reached, a few miles above Aldrich's mine, touching and taking 

 off a small corner of Whiteside county. All of Bureau and Henry coun- 

 ties south of this line are underlaid by lower Coal Measure deposits. 



A line passing through the points where coal is actually worked along 

 the north margin of the Illinois coal field, would pass across the State 

 from Eock river to the Illinois, as follows : Commencing at Aldrich's 

 mine, on Eock river, thence south-east to Anawau, on the Chicago and 

 Eock Island Eailroad ; thence nearly east on the same road to Sheffield ; 

 thence to the shaft of Eobinson, Uinks & Co., near the crossing of the 

 railroads between Wyanet and Buda.; thence north of east to Bierinau's 

 shaft, five miles east of Princeton ; thence to the shafts and outcrops 

 about LaSalle and Peru. Coal may yet be worked north of this last 

 line, but at all events, the coal deposits extend as far north as the first 

 described line. 



It will thus be seen that over two-thirds of the county is underlaid 

 by the Coal Measures. Having given their superficial extent, let us next 

 obtain as good a vertical section as we can. Two artesian wells, one 

 put down at Princeton and one at Tiskilwa, afford the best opportuni- 

 ties of making such a section. These wells are not always reliable, but 

 they furnish the best data that can be obtained in this county : 



Section of Artesian Well at Princeton. 



1. Soil, and yellow and blue clays 53 feet. 



2. Sand.. 20 " 



3. Clay, indurated hard-pan 3 " 



