Dr. D. Dale Owen on the Geology of North America. 181 



ing a short distance into Jowa. It is covered on the north by ex- 

 tensive diluvial deposits, sometimes to the depth of more than a 

 hundred feet. The other coal-field forms a part of at least six states, 

 viz. Ohio, Kentucky, Tennessee, Pennsylvania, Maryland, and Ala- 

 bama ; and its area is estimated at 50,000 square miles. These 

 coal formations consist, as in Europe, of sandstones, shale, slaty 

 clays, seams of coal, and occasionally beds of limestone, these latter 

 usually dark- coloured and bituminous. At the base of the Ohio 

 formation is a conglomerate from 200 to 300 feet in thickness, which 

 has been referred to the millstone grit of England. A similar con- 

 glomerate shows itself in one or two localities at the base of the 

 Illinois coal-field. 



The thickness of these coal-fields is estimated at from 1200 to 

 2000 feet. All the coal is of a bituminous character, some of the 

 caking variety, some splint coal, some cannel. Neither of the coal- 

 fields have suffered much from dislocation ; no dykes of trap, whin- 

 stone, basalt, or greenstone have been met with in either. On the 

 eastern flank, however, of the Cumberland mountains, the coal is 

 occasionally much disturbed, even thrown up nearly vertically. There 

 is a striking analogy between the fossil flora of these western coal- 

 fields and that of the equivalent strata in Europe. The most pro- 

 ductive brines discovered in the western states have been procured 

 by boring through the lower members of the coal measures. Imme- 

 diately below the coal-formations of Indiana, Illinois, Kentucky, and 

 Tennessee, are limestones mostly of a light gray colour and of a 

 compact texture, including occasionally layers and nodules of chert. 

 Some of these limestones assume the appearance of lithographic 

 stone, others present a beautiful oolitic structure. The strata vary 

 in thickness ; in Ohio it does not appear to exist, being replaced by 

 the before-mentioned conglomerate. The great mammoth cave of 

 Kentucky is in the upper beds of this limestone, which abound in 

 subterraneous passages. These beds are characterized by two re- 

 markable fossils, the Pentremites and the Archimedes, and Dr. Dale 

 Owen has designated the group Pentremital limestones, from the 

 abundance of those fossils. The oolitic stratum lies immediately 

 beneath. No workable seam of coal has hitherto been found beneath 

 the beds containing these fossils ; Products and TerebratulcR are 

 abundant in them, and a small species of Calymene occurs. Dr. Owen 

 regards these limestones as the equivalent of the mountain limestone 

 of Europe. Iron ores occur at the junction of the limestone and coal 

 measures, and galena and fluorspar have been found in the former. 



The rocks which succeed to the Pentremital limestone are gray, 

 yellow, and brown siliceous sandstones, soft and fine grained, some- 

 times argillaceous and free from mica, passing on the one hand into 

 chert and limestone, and on the other into a rock presenting the 

 appearance of Tripoli : interstratified with these are beds of lime- 

 stone, occasionally oolitic. This group is not rich in organic re- 

 mains ; Crinoidece, Polypiferce and Products are most common. The 

 middle and lower beds of this group are regarded by Dr. Owen as 

 probable equivalents of the upper Ludlow rocks. 



