CAKBONIFEKOUS SYSTEM. 283 



with a locally developed bed of limestone intervening; ten 

 feet and npwards. 



In the counties of Guthrie and Warren, the last described 

 bed is well-marked, presenting essentially the appearance 

 represented in the foregoing general section. But in Madi- 

 son and Appanoose counties, we find a coal-bed beneath 

 well recognized Upper coal strata, which is thought may 

 prove to be the equivalent of the upper bed, or Lonsdale 

 coal, of the Middle coal 'formation. In the latter region the 

 coal is associated with two limestone beds, one above and 

 the other below, besides the arenaceous deposit at the base of 

 the Upper coal-measures, as shown in the Winterset section, 

 is entirely replaced by argillaceous shales and limestone 

 bands, as shown in the general section of the rocks in Appa- 

 noose county. If the above intimated identity exists, the 

 horizon has not only entirely changed its lithological aspect, 

 but the fossils of the associated bituminous shales have little 

 resemblance, that forcibly recalls the Lonsdale coal as it 

 appears in the northern portion of the Middle coal area. 



4. ECONOMICAL GEOLOGY. 



Coal. By far the most important mineral product of the 

 Middle coal-measures is coal. As has been already stated, 

 these deposits are quite limited compared with the coals of 

 the productive or Lower coal-measures. But, at the same 

 time, their quality seems to be superior to that of the heavier 

 beds in the latter formation; and for this reason, if on no 

 other account, these beds will be mined for a long time on a 

 more or less extensive scale, at least, for the supply of the 

 local demand for those purposes which require a pine coal. 

 Some of the beds are locally of sufficient thickness to be 

 regarded as "workable." But it is not unusually the case 

 that twelve-inch beds are quite extensively mined, as in the 

 instance of the Panora coal. The Lonsdale coal is the 

 thickest and most regular of the persistent coal-beds in the 

 formation, and being unusually free from admixture with 

 impurities, it will become an important resource for fuel in 



