C A R U 0 N I F E R 0 U S LIMESTONES OF I 0 W A. 



99 



direct line, nearly two hundred miles, in a northwesterly direction, up the valley 

 of the Des Moines.* 



It is bounded by an irregularly undulating line, as follows : commencing where 

 the line between Iowa and Missouri crosses the Des Moines River, near the west 

 border of Lee County ; thence, nearly north, to the northeast corner of Washington 

 County ; thence, with a northwesterly curve, to the Iowa River, which it crosses 

 in Township 81 north, Range 8 west, of the 5th Principal Meridian, not far from the 

 line between Johnson and Iowa Counties ; thence, up the valley of the Iowa, some 

 twenty-five miles, when it recrosses that river, near the southeast corner of Tama 

 County; thence, curving through Tama County, and again crossing the Iowa, to 

 near the centre of the east line of Marshall County ; thence, along the water-shed 

 of the Iowa and Cedar, recrossing the former near the northeast corner of Township 

 87 north, Range 30 west, of the 5th Principal Meridian ; thence, with a westerly 

 curve, up the Iowa, and continuing west of that river to the " Big Woods," where it 

 recrosses, for a few miles, returning to the west side of that stream, and running in 

 a nearly due west course to the Des Moines, which it crosses six miles above the 

 Lizard Fork ; thence, with a southwesterly curve, towards the head-waters of the 

 Three Rivers ; thence, down the valley of Ncshnabotna, to the State line. 



It is to be remarked, that this boundary line was, in some places, of difficult 

 determination ; and, especially in the north and west, obscure and ill-defined for 

 considerable distances ; chiefly on account of the depth and extent of the superficial 

 sedimentary deposits. 



Along the course of the Mississippi, the belt of Carboniferous Limestone cannot 

 be traced north much beyond its confluence with the Iowa. Here it is lost beneath 

 sandstones of the coal-measures, which appear in the Muscatine bluffs, and are 

 remarkable, as well for the fine specimens of Lepidodendrons and Ferns which they 

 afford (see Table VI., Figs. 1, 2, 3, 4, 5, G, and 7), as for the globular form and 

 great size of the curious segregations of argillaceous sandstone, which are shown in 

 the subjoined wood-cut, as they have been laid bare in one of the quarries, half a 

 mile below the town of Muscatine. 



About five miles below the mouth of Pine Creek, these carboniferous sandstones 

 are succeeded by limestones belonging to the Devonian period ; they reappear, how- 



* After crossing the Iowa boundary lino into Missouri, the boundary line of tins coal-field bears nearly 

 south, through Clark, Lewis, and Marion Counties, to near the junction of the Three Forks of Salt River. 

 Thence through the western part of Ralls County, towards the head waters of Riviere au Cuivre, in the 

 eastern part of Audrain County, and northwestern corner of Montgomery County. Thence it sweeps, in 

 a southwesterly curve, through Calloway County, towards the Missouri River, which it crosses near its 

 confluence with the Osage; leaving a belt of country, some ninety miles wide, between this coal region 

 and the outcrops at Charbonnicre, and the coal-pits worked on Riviere des Peres, in St. Louis County. 

 These are, in fact, outliers of the Illinois coal-field. From the Missouri River the boundary bears, with 

 a westerly curve, up the valley of the Osage, north of that river, which it crosses, but for a very limited 

 distance only, at three points : in Camden County, near the mouth of the Niangua ; in St. Clair County, 

 near the mouth of Sac River; and in Bates County, near the confluence with the main river of the Little 

 Osage. Thence the line bears, with a northerly curve, towards the western confines of Fayette, recrossing 

 the Missouri at Wellington ; thence up the valley of that river, keeping from ten to twenty-five miles 

 from the river, to the State line. 



