no The American Geologist. August, 1902. 
1744 in Charlevoix's great work, "Histoire de la Nouvelle 
France.'' Between the dates represented by these maps, the 
south pass had been much extended, while the others showed 
little change. 
After these early dates, until 1885, when the admirable 
maps of the lower part of this river from surveys of the 
Mississippi River Commission were issued, each of the passes 
.was extended six to eight miles into the gulf, and the eastern 
passes became more complex, with broad adjacent mud fiats. 
Humphreys and Abbot, in 1861, determined the average yearly 
advance of all the passes to be 262 feet, which would amount 
to about five miles in a hundred years ; and they estimated 
that a period of about 4,400 years has been occupied by the 
extension of the delta from the vicinity of Plaquemine and 
the Bayou Manchac. 
When the delta was seen by Vespucci, four centuries ago, 
it probably terminated ten to fifteen miles back from the pres- 
ent head of the passes, where an old branching delta front is 
shown by the map of the Mississippi River Commission, in 
the continuation of the curving line of the Chandeleur islands 
and Breton island. 
The extension of the delta from the old to the new group 
of branches or passes was eftected evidently by the enlargement 
and elongation of one of the former passes far beyond the 
others, untij it gradually became the chief channel, and was 
finally the only channel at ordinary stages of the river. Then, 
or during the latter part of that extension and widening, a 
new trifnrcation took place at or near the end of the greatly 
elongated pass, there establishing a new s_ystem of distribu- 
taries, similar to the previous system that was thus abandoned 
and left about fifteen to twenty-five miles in the rear, its old 
channels being filled with river silt. Probably this process of 
periodic extension, new forking, and reinstatement of passes 
and mouths had taken place only once before the present system 
came into existence. 
Inspecting the convex general coast line of the delta, from 
Mississippi sound southwestward across the present course of 
the river, and onward west and northwest to Atchafalaya and 
Vermilion bays, we see how the delta was gradually built out 
into the gulf to that limit, growing forward, similarly with many 
other deltas of large rivers, upon a curved coastal tract two 
