R. L. Moodie — Mazon Creek Shales. 2S3 



At the " lower beds" (figs. 3, 4), so-called because farther 

 down the creek, conditions are quite different from those just 

 described. The west bank of the creek is higher and almost 

 perpendicular, and the east bank is low and flat, the bluff 

 being a quarter of a mile away, so that the chances for collect- 

 ing from the shales are fewer. The bed of the creek, however, 

 is wider and there are more nodules washed out. The most 

 abundant fossil at this place is Neuropteris. The nodules at the 

 upper end of the exposure are all, almost without exception, 

 barren of fossils. The exposures here are of about the same 

 thickness and extent as the "upper beds," though the species, 

 contained in the nodules, are not so varied. Judging from 

 the collections made while there, the Arthropoda are the more 

 abundant in the lower beds. This is, however, a matter which 

 needs further investigation. 



Besides the place near Morris mentioned by Bradley there 

 are no other localities known where the nodules are collected. 

 Bradley* says of the Mazon Creek beds : "The outcrop (i. e., 

 the Coal Measures) along Mazon Creek appears nearly continu- 

 ous, but still I have not been able to satisfy myself as to the 

 connection of the above beds with, those of the lower part of 

 the stream. The strata there developed consist of very variable 

 sandy clay shales and sandstones, in some places becoming 

 nearly pure clay shales, but containing many nodules of car- 

 bonate of iron. Pine Bluff, at the lowermost crossing of the 

 Mazon, is composed of about forty feet of heavily bedded but 

 rather fissile sandstone, partly nearly white, partly nearly 

 ferruginous. Less than a mile up the creek, the lower part of 

 this bed changes to highly argillaceous sandy shales, with 

 occasional streaks and nodules of sandstone. The section is 

 not quite continuous, but there is no distinct line of deinarka- 

 tion to separate these latter beds from the ferruginous sandy 

 shales, twenty or thirty feet, of section 24, of township 33 

 north, range 7 east, which contain large numbers of the fossil- 

 iferous nodules of carbonate of iron, for which this locality has 

 become famous. * * * * These nodules range from about 

 two to ten feet above the main coal seam of all this region, 

 the intervening space being occupied by the soft, blue clay 

 shales, filled with fossil plants, which, at most points, overlie 

 this seam. About a mile farther lip the stream, coal has been 

 dug in the bed and banks of the stream but is now abandoned, 

 -x- * * * Q n f.j ie nor th s id e f the Illinois river, in the neigh- 

 borhood of Morris, the coal outcrops in the banks of the canal, 

 and in the stretch of lowland about one mile to the northward. 

 The overlying beds are here mostly blue clay shales, with 

 occasional irregular layers of sandstone. The iron nodules 

 * Geol. Surv. Illinois, IV, pp. 196-7, 1870. 



