1847.] LYELL ON THE NUMMULITE LIMESTONE OF ALABAMA. 13 
The American fossil therefore now under consideration will hence- 
forth be called Orbitocdes Mantelli, retaiming the specific name first 
given to it by Dr. Morton. 
In my former paper I endeavoured to point out the cause of the 
obscurity in which the true age of the nummulitic or orbitoidal lime- 
stone of Alabama had been involved, it having been considered some- 
times as an upper cretaceous group, and at others as intermediate 
between the cretaceous and the Eocene formations. The accompa- 
nying section from Claiborne Bluff to Bettis’ Hill near Macon in 
Alabama may serve to explain the relations which I found to exist 
between the white limestone group of the south, comprising the suc- 
cessive formations 1. 2. 3, and the overlying group 4, which is per- 
haps of equal thickness, but which, from the absence of calcareous 
matter, rarely yields organic remains, and those consisting only of sili- 
cified casts of shells and corals. This upper formation (4) is com- 
posed of variously coloured red, pink and white sands, and yellow 
ochreous coloured sands, white quartzose gravel and sand with beds 
of chert and flint, blood-red and pink clays, and clays of white kaolin 
or porcelain earth, all horizontally stratified. I could find no fossils 
in those in Alabama, and only conjectured that they are of Eocene 
date from the analogy of Georgia, where a deposit of the like aspect 
and nature and occupying a similar position contains Eocene shells 
and corals. I formerly explained in 1841—42 the relative position of 
the upper clays and sands with flint (the Burr-stone formation of 
Georgia) to the underlying white limestone and marl of the State of 
South Carolina, in a diagram published in the Journal of the Geol. 
Soe. vol. i. p. 438, where the newer group is represented as resting 
on the eocene limestone of Jacksonborough near the Savannah river. 
It appeared in that case as in Alabama, that the older calcareous strata 
of limestone and marl had undergone great denudation, and had ac- 
quired a very uneven surface, having been shaped into hills and val- 
leys before the incumbent clays and sands were thrown down. 
At the bluff on the Alabama river at Claiborne, where so rich a 
harvest of fossils has been obtained, especially in the beds of No. 2, 
we see at one spot called «The Old Landing,” that nearly the whole 
precipice in its lower 160 feet, exposes to view the calcareous beds 
1. 2. covered with about 20 feet of red clay and sand, whereas at the 
distance of less than a mile from this spot, the upper formation No. 
4 occupies more than 100 feet of the face of the same cliff from its 
summit, while at the base the lower members of the calcareous series 
crop out from beneath the horizontal and mcumbent beds of sand 
and clay. This twofold composition of the mass of strata in the 
bluff at Claiborne is expressed at A in the annexed woodcut, and 
I verified a similar mode of juxtaposition of the two series of beds 
in several places in the interior of Clarke County, where the lime- 
stone often ends abruptly, and is succeeded sometimes in the same 
ridge or hill by the newer beds (No. 4), the latter having evidently 
filled up the imequalities of a previously denuded deposit, after which 
the whole was again denuded. 
I have suppressed several details and repetitions of the same phzeno- 
