168 On the Gnathodon beds around the head of Mobile Bay. 
shore. They mark the period of the last retreat of the water 
within its present more circumscribed limits. Their former sub- 
merged condition, must evidently have corresponded with that 
of those which are still found living in a littoral situation. The 
abrupt termination of these masses, without the appearance of 
any scattered remains in the interval between them and the 
shore, likewise the absence of living individuals in the neighbor- 
ing water, will not seem surprising, when it is considered that the 
current, caused by the more contracted limits of the channel, 
must have prevented their continuous multiplication. There are 
however, some instances, where thinly scattered remains occur 
even to the water’s edge, but such cases are found only in cit- 
cumstances which are favorable for the continued existence of 
the species. 
“he beds of this class are generally two or three yards above 
the level of the tide. The foundation on which they rest resem- 
bles that of a submerged bottom, not that of an open bay,—rather 
like that of an estuary in the vicinity of rivers and inlets, where 
the siltings of fresh-water alluvinms are not wholly excluded. 
Those deposits which occur on the Mobile and Tensaw rivers 
are evidently of a much older date than those already noticed in 
the intermediate space, which must have remained longer in @ 
condition unfavorable for the propagation of the species. 
That series of inland deposits west of Mobile bay, commenc- 
ing at the northwest angle of that bay near Choctaw point, an 
extending northwardly to Twenty-one mile bluff, presents several 
largest and most elevated masses are found; they also mark in @ 
very striking manner, the former inland extent and shore-line of 
the present bay. It is also observable that the largest of these 
deposits usually occur near the outlet of some stream, where eX- 
isted a favorable combination of circumstances for their increase, 
particularly the confluence of the fresh-water current with the 
ocean tide. Instances of a similar nature are presented along 
the borders of that chain of lakes, connecting with the Gulf of 
Mexico, and extending into the southeast section of Louisiana, 
especially the one which formerly existed at the mouth of Blind 
river, it is more than twenty feet high and six hundred yards in 
length. ‘ 
Before proceeding to the examination of our last object of 1n- 
quiry, the structure and contents of these beds, it will be proper 
to notice the distinction which ought to be made between cer 
tain effects of Indian agency, and those which are the wee 
natural causes. eae 
It is evident that at some former period these shell deposits 
were objects of much interest to the aborigines. They seem tO — 
