OF THE UNITED STATES. Zo 
formed of the nummulite limestone, masses of which are 
scattered in every direction: it is porous, or contains 
spheroidal cavities, formed no doubt by the decomposi- 
tion of organic remains, which leave loose casts that are 
easily washed out by the rains. The most characteristic 
fossil at this place is Ostrea panda. 
‘¢ These limestone hills occur at intervals to the vicinity 
of Jackson, on the Tombeckbe: on Basset’s creek one of 
these hills rises probably to a height of 300 feet above the 
water level. JI crossed the river at Jackson, which is on 
a high sloping bluff, entirely diluvial, and proceeded over 
a succession of pine covered hills until within a mile of 
St. Stephens, where the limestone again appears. St. 
Stephens is on a high bluff of this rock, which, wherever 
it occurs, forms a very broken or undulating surface. A 
short distance above the village, the bluff rises nearly 
perpendicular from the river, and is about 100 feet high. 
Every where in the vicinity this limestone crops out on 
the summits of the hills, and myriads of Mummulites 
Manteilt are scattered over the surface of the decom- 
posing rock. The Gryphza vomer is occasionally found 
among them, and the Ostrea panda is abundant, but no 
other fossils occur excepting what are peculiar to the 
limestone in question. On the hills I observed the Pec- 
ten Poulsont in abundance. Near low water mark in 
the bluff is a stratum of shells consisting of Ostrea panda 
and Plagiostoma dumosum, both equally abundant. The 
surface of this rock is in many places very hard, and of a 
bluish color, compact, and glittering when fractured, 
and is convertible into excellent lime. Again it is often 
