DALE OWEN ON THE WESTERN STATES OF NORTH AMERICA. 4-37 



western and south-eastern terminations of this basin it is well-de- 

 veloped, being from 200 to 300 feet in thickness. On the western 

 slope of the Cumberland mountains in Tennessee, Dr. Troost found 

 it generally about 200 feet thick. 



In Ohio these limestones do not appear to exist, at least they have 

 not yet been detected, and the conglomerate before-mentioned oc- 

 cupies their place. The most extensive caves and subterraneous 

 passages in this country are in these limestones : the ' Mammoth 

 Cave ' in Kentucky, which has been penetrated to the distance of 

 six miles, is situated in the upper beds of this limestone. Lost River 

 in Orange county, Indiana, disappears from the surface for many 

 miles, and flows through subterraneous passages in the same rocks, 

 and so also do several streams in Kentucky in the vicinity of the 

 Mammoth Cave. 



The upper beds of the rocks under consideration are characterized 

 by two very remarkable fossils, the Pentremite and the Archiiiiedes, 

 Four species, at least, of Pentremites have been observed in the 

 oolitic beds : P. pyriformis ? *, Say ; P. globosa. Say ; P. florialis. 

 Say ; and P. ovalis, Goldf. From the abundance of these fossils, 

 I have been accustomed to designate this group of rocks by the 

 name of Pentremital limestones. The Archimedes \, Lesueur, oc- 

 curs in a bed of limestone of a reddish-yellow cast, the uppermost 

 bed of the series, and the one on which the lowest members of the 

 coal-measures rest. The same stratum often contains Pentremites. 

 The oolitic stratum lies immediately beneath. No workable seam 

 of coal has hitherto been found beneath the beds containing these 

 fossils : they become therefore a trustworthy guide in determining 

 the limits of our coal-formations. 



Stylina Peroni^ Lesueur, and another species of Stylina are also 

 characteristic of these rocks. Syringopora (ramulosal)^ Goldf., is 

 not uncommon in Tennessee and Missouri. I have also obtained a 

 fossil from Terry county, Indiana, having the general aspect of a 

 Trilobite, yet not divided into three lobes. Bellerophon hiulcus is 

 considered by Dr. Troost as a characteristic fossil, and near Eddy ville 

 in Kentucky lie found specimens between five and six inches in length. 

 There is also a coralline different from any I have seen described in 

 Goldfuss or elsewhere, having large and distinct cells of a truncated 

 cup-shape, and disposed in alternating lines. I have named it Cya- 

 thopora lowensis: it was obtained in a rock in Iowa, probably a 

 member of this group. 



It has been asserted that no Trilobites occur in these limestones ; 



* This Pentremite differs a little from the drawing of P. pyriformis which 

 I have seen ; it is more angular or pointed where the interscapula joins the am- 

 bulacrum, and the striaj of the ambulacrum run slanting from above downwards, 

 from the central furrow towards the interscapulaj, instead of from below up- 

 wards. 



t I am not sure that Lesueur ever published his description of this fossil, but I 

 know that while he resided here (at New Harmony) he engraved a i)late contain- 

 ing several views of it with that intention. He considers it, I believe, a new 

 genus, but it may be only a new species of Retepora ; if so, it would be most aptly 

 entitled Retepora Archimedes. 



