292 



scriptions by the geologists of those States, and others. At these 

 places the Burlington Limestone holds its position and retains its 

 characters with remarkable constancy, and the other , members of the 

 Carboniferous Limestone series, above it, are well defined. But 

 passing to the eastern outcrop of these carboniferous rocks, on the 

 west side of the Cincinnati axis, we find the Burlington Limestone, as 

 such, entirely wanting, and the lines of subdivision of the other mem- 

 bers of the Carboniferous Limestone series usually less distinctly 

 marked than along the Mississippi river, while the beds which have 

 been referred to the Chemung group have undergone so great a 

 change as to be scarcely recognized by lithological or paleonto- 

 logical characters. 



Starting at the Muldraugh's Hill range, where it is crossed by the 

 Louisville and Nashville railroad, going in a northerly direction, pass- 

 ing " the knobs " in Kentucky, New Albany, New Providence, and 

 thence as far north as Montgomery county, Indiana, we find a series 

 of sandy shales resting upon the " Black Slate," which extend upward, 

 and gradually mingle with the Carboniferous Limestones. The lower 

 part of this mass has, so far as we know, afforded too few fossils to 

 designate its age, but which has heretofore been considered equivalent 

 to the Chemung of New York. As we pass upward, however, we 

 begin to find carboniferous fossils, and so far as we have examined 

 them, they approach more nearly in character to those of the Keokuk 

 Limestone than to those of the Burlington Limestone, or those of the 

 Chemung rocks of the Mississippi Valley ; but barely enough of the 

 fossils of the Burlington Limestone are recognized there to show that 

 it is represented. 



When we see that a formation, so well developed as in the Burling- 

 ton Limestone, can undergo such great changes in a distance com- 

 paratively so short, we need not be surprised to find the great differ- 

 ence which exists between the Chemung rocks of New York and 

 those of the JMississippi Valley. 



DESCRIPTION OF NEW SPECIES. 



BRACHIOPODA. 



Genus Orthis, Dalman. 

 Orthis subelliptica (n. sp.) 



Shell of medium size, subelliptical in outline. Hinge line about 

 two-thirds or three-fourths as long as the greatest breadth of the shell. 

 Cardinal extremities rounded, valves subequal, moderately convex ; 



