166 GEOLOGY OF ILLINOIS. 



Above the north line of section 21, the bluffs, for about two miles, are mostly 

 of Loess, and it is necessary to go up the side ravines in order to see the ex- 

 posures of rock. About half a mile up the large ravine, which cuts through 

 the bluffs in the southern part of section 10, I observed on the eastern side, 

 another exposure of the sandstone, (No. 2 of the section) and a little above 

 this, near the northwest corner of section 14, I also noticed about ten feet ex- 

 posed of the shales No. 4, capped by a single layer of limestone, two feet thick, 

 (No. 3). The coal seam must be very near the bottom of the ravine at this 

 point, but it is not exposed. The outcrops of the sandstone continue up this 

 ravine and its branches, in the eastern part of section 14, and the western part 

 of section 15, for about three-quarters of a mile above this point, and then dis- 

 appear entirely. The rock is, in most respects, the same as in the localities 

 before described, a soft, even textured sandstone, varying in color from brown- 

 ish red to a dirty white, and in some portions having a light bluish tinge, and 

 a slightly variegated appearance. It contains a great abundance of fossil vege- 

 table remains, Calamites, etc., but from the nature of the rock, very few are 

 found in a good state of preservation. 



From the mouth of this ravine, for a short distance to the northeast, along 

 the face of the bluffs, there are no very good exposures of any of the beds. 

 There seems to be here, however, a low anticlinal. The strata having gradu- 

 ally risen, until at this point, the coal seam No. 4, has been worked by drifting 

 into the side of the bluff almost midway between the base and summit. The 

 crown of the arch is very near this point, and the direction of the axis of the 

 fold must be, judging from appearances, about southeast. The vein of coal is 

 said to be about three feet thick at this point, but at present only the entrances 

 to the old drifts, and the debris can be seen, no work having been done here 

 for a number of years. 



A short distance further along the bluff road, nearly on the line between 

 sections 10 and 11, another large ravine opens out, and the rock again appears. 

 The coal seam was formerly worked also at this point, at a level some fifteen or 

 twenty feet above the road, though its outcrop is not now visible. Just below 

 the level of the old drift, I observed an outcrop of what appeared to be a nodu- 

 lar argillaceous limestone, which I take to be just underlying the fire clay. 

 Above the opening of the drift, the shale No. 4, appears, and still higher up 

 the bank, the limestone No. 3, has been slightly quarried, and above all the 

 sandstone, No. 2 appears, but at present the debris of the sandstone and shale 

 covers all the lines of junction, and no very reliable measurements of the thick- 

 ness of the beds can be taken. The sandstone continues to appear in the sides 

 of the ravine, and in the bed of the small stream which occupies it, for up- 

 wards of half a mile. Its total thickness, although in no place so fully exposed 



