Submarine Valleys and Canons off American Coast 
Before reaching the ocean, the rivers everywhere pass over valleys many miles in width, refilled by 
Pleistocene (or possibly late Pliocene) loams, sands, or gravels. These valleys are excavated out of earlier 
Tertiary formations. The depths of the channels are not known, but borings show that of the Savannah 
River to reach at least 250 feet below sea-level. Borings made in the Tertiary limestones of Florida 
have already revealed caves to a depth of 800 feet or more. These were the underground river channels 
which carried off the surface drainage when the land was high. Such were mentioned by Professor 
N. S. Shaler as evidence of the recent depression of Florida. 
After passing the sand-filled stretches of the submerged valleys, these again become apparent in 
crossing the Continental Shelf and lower plateaus, from which they descend through great cafions, and 
enter embayments of the ocean basins. Their walls are often precipitous and reach to thousands of feet in 
depth. 
The Buried and Submerged Valley of the Mississippi—On the northern side of the Gulf of Mexico, 
outside of the shifting sand zone, all the principal rivers of the Southern States show their valleys 
continuing to depths of 10,000 feet. The Mississippi River, above its mouth, is 200 feet deep, while the 
sandbars in front almost block the channel. Here are also other submarine channels with their upper 
extensions refilled, so that they do not reach to the land, nevertheless they show where the rivers 
formerly ran. 
The valley of the Mississippi, for 500 miles above its mouth, is a plain from 30 to 80 miles wide, 
which was liable to overflows before the river banks were diked. By borings at New Orleans, Corthell 
found, at least, 1000 feet of river silts and Pleistocene loams, without reaching the bottom of the 
channel. 
The depth of the buried valley of the Mississippi is thought by Professor G. D. Harris to be 3000 
feet. This inference is based upon borings for salt some distance to the west, which show buried valleys 
or amphitheatres 2300 feet deep in the now submerged plateau. These increase in depth in passing 
eastward. Pleistocene shells are the only organisms occurring in the filling of the valleys which are 
excavated out of Tertiary deposits with underlying Cretaceous formations. ‘This is the positive palaeonto- 
logical evidence of a late high continental elevation, confirming my views regarding systems of submarine 
valleys which were later submerged. 
The Submerged Floridian Channel and Cafion—The Floridian Channel extends from the Straits of 
Florida, with a depth of 2100 feet, to the floor of the Gulf of Mexico, at 12,000 feet,—a distance of 400 © 
miles. The descent is by three principal long reaches of low gradient, separated by abrupt steps, each 
reach of which is incised by a cafion 3000 feet deep, opening on the valley floor below. This is the 
grandest submarine valley explored. The length is a great advantage in studying its development. 
There are several important tributaries besides many shorter ones of amphitheatre form. To the west- 
ward of its mouth is also the fine cafion of the Yucatan Channel, which is now submerged to its head. 
The Bahama Banks and their Valleys—Leading from the Straits of Florida, the Abacan Cafion (see 
Map) dissects the Bahama Banks between two of the islands; and the Bahaman Channel leads from 
the northern end of the Straits of Florida into the deep cafion separating the Bahama Banks from the 
submerged Continental Plateau. 
The Bahama Banks are further dismembered by entirely submerged valleys heading in amphitheatres. 
These were partly explored by Professor A. Agassiz, who, however, did not understand their origin. The 
low Bahama Islands are covered by coral sand resting on Mid-Tertiary limestones. Immediately in front 
of the banks, the descent to the oceanic abyss is very steep, so that if the region were high, the tropical 
rains would rapidly excavate deep wash-outs or amphitheatres, even though no long rivers were flowing 
through them. Indeed, the absence of long rivers would favour the relatively greater breadth of the 
valleys, as compared with their length, These deep valleys suggest no other relationship than gigantic 
wash-outs or amphitheatres, in front of high tablelands, made by rains, rills, and rivers. 
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