DALE OWEN ON THE WESTERN STATES OF NORTH AMERICA. 439 



dom however extending uninterruptedly over any considerable area. 

 Some of these are occasionally oolitic, and the lower part of the 

 series is more argillaceous than the upper, passing in some places 

 into a slaty clay. The range, extent and bearings of the rocks in 

 question may be seen by reference to the map, and their position 

 beneath the Pentremital limestones is shown on the section. To the 

 N.W. this rock runs out, at least I was not able to detect it in Iowa 

 and Wisconsin. To the east and south it is chiefly developed, being 

 150 to 300 and even 400 feet thick. 



As a whole, this group is not rich in organic remains. Crinoidea, 

 Corals and Productee are the most common. One species of Pro- 

 ducta occurs in the upper beds, and others some 50 or 100 feet 

 lower in the series. The Gorgonia is a fossil very characteristic of 

 the middle beds, and a large Delthyris belongs to them. Remains 

 of Dicotyledonous plants have also been found in them. 



In Tennessee Dr. Troost has found in this group of rocks Gor- 

 gonia antiqua, Goldf., a Pinna (species undetermined), a Terebra- 

 tula (species undetermined), and hexagonal plates of Echini. A 

 LeptcRua occurs about 100 feet above the base of this group. 



The interstratified limestones in Tennessee are often rich in Cri- 

 noidea, and in comminuted remains of Gorgonia, Retepora, Cerio- 

 pora and Eschara. So few and ill-defined are the fossils of this 

 group, where I have had an opportunity of studying them with at- 

 tention and making collections, that it becomes difficult for me to 

 pronounce with confidence on its European equivalents. From the 

 occurrence of several species of Producta in the upper 100 feet, and 

 their absence in the lower beds, it is not improbable that they ought 

 to be designated as two distinct groups. Mr. J. Hall of New York 

 has referred the upper 100 feet to the Old Red or Devonian system, 

 but no satisfactory evidence has been brought in proof of this re- 

 ference. No vestiges of Holoptychius or Cephalaspis^ or other fossil 

 fish, have, to my knowledge, been found in it. 



In the absence of such palseontological evidence, and on account 

 of its resemblance in lithological character to the underlying strata, 

 and the almost imperceptible blending of the adjacent strata, I have 

 not for the present thought it advisable to separate them. The 

 middle and lower beds of this group are probably the equivalents 

 of the Upper Ludlow rocks of Murchison's ' Silurian System.' 



The Portage, Chemung and Ithica sandstones of the state of New 

 York have been referred to this group, and the colossal deposits of 

 hydrated brown oxide of iron, so extensively wrought in Tennessee, 

 are associated with the same rocks. In Tennessee this series usually 

 rests on Encrinital limestone (the uppermost bed of the succeeding 

 group). It is above this limestone, and amongst the overlying sili- 

 ceous deposits, which usually then assume the nature of chert, that 

 the above-mentioned iron ore has been discovered imbedded in a 

 tenacious clay. The same order of things exists in Jefferson county, 

 Kentucky, and in the base of the Knobs of Floyd county, Indiana, 

 where beds of conglomerate iron ore occur in slaty clay. Small 

 quantities of gypsum have been found in nests, in fine greenish- 



