Submarine Valleys and Cafions off American Coast 
Concerning the great Agave family, Dr. William Trelease, after long investigation, expresses 
conclusions of which he has no doubt. He says that their seeds could not have been carried across even 
narrow channels of water, and “ that they went dry-shod from Cuba around the West Indies to Venezuela.” 
He is convinced that Cuba was the primary centre of their distribution. It is immaterial whether 
they made a short circuit by way of the Lesser Antillean Plateau, or followed the longer route by way 
of Central America. The Jamaican and the Haitian species are more closely related than those of 
Jamaica and Cuba. This is what should be expected, for Jamaica and the south-western ridge of Haiti 
are continuous, with their land-tongues submerged to probably much less than 6000 feet. But Jamaica 
and Cuba are to-day separated by the deep trough of 18,000 feet, which dates back to a time prior to the 
Pleistocene period. 
As has already been stated, the passage between Cuba and Yucatan, with its sides incised by cafions 
and land-features (indicating the former elevation), is at the same depth (6400 feet) as the Anegada 
Channel, among the Virgin Islands. Accordingly, a change of level which would have permitted of the 
migrations of the Agave in one direction would have been sufficient in the other. From the occurrence 
of Amblyrhiza in St. Martin, the biological evidence proves that the Pleistocene elevation in the east was 
more than 3500 feet. Such an elevation would have also joined the islands to North America, as the 
deepest land-tongue between the Bahamas and Florida is now submerged only 2100 feet. To question 
the former land connection here, while admitting the extension of Cuba to Central or South America, 
would be simply an evasion. 
In Southern Florida and in the Islands there are related land shells, and also plants (Dr. R. M. Harper)." 
Results establishing Changes of Level of Land and Sea.—In the plateau regions, cafions are found 
within cafions,? showing former changes-of drainage level. In their courses they meander and make 
many sharp turns. Their: descent is by a succession of steps such as produce rapids and waterfalls, the 
lowest being the newest. As the waterfalls are developed, the higher and older ones continue to recede, 
but their retreat may be faster or slower, so that the great steps become farther apart or come together 
or unite. All of these features are found in the submarine cafions studied. We know of no great open 
fissures like these valleys and cafions, except such as are produced by streams, although joints and cracks 
may have caused their location and facilitated their excavation. Hence the natural explanation is that 
those beneath the sea were land-valleys, although now submerged. 
I was once asked if the formation of these gorges by tidal currents had been considered—that is, 
if tides acting hundreds or thousands of feet below the surface of the sea could produce cajfions and valleys, 
associated with terraces. It seemed like a last effort to evade the evidence of great changes of level. 
However, the ocean currents are worthy of consideration, although they commonly sweep crosswise of 
the submerged valleys, which could not be affected thereby. Some others, such as the Gulf Stream, flow 
in the direction of the submerged channels, but this loses its velocity and abrading action.at about 300 
feet below the surface. I have also shown, on a previous page, how the Gulf Stream has not planed 
off the floor of its physiographic summits. 
The wide channels between the islands are commonly across the ridges, although sometimes parallel 
with them, As their lateral slopes are also incised with cafions and amphitheatres, it is evident that they 
were not fashioned by ocean currents. This feature also shows that the depressions between the islands 
are not due to block subsidence, for they must have been elevated during the formation of the lateral 
valleys. The rolling features of these wide channels were formed earlier than the cafion-making epoch, 
but after the Mid-Tertiary period. The submarine platforms and the land-tongues, repeated at the 
similar depth over widely separated localities, become further evidence in favour of late changes of sea-level. 
1 Dr. Roland M. Harper has kindly furnished me with a list of 70 species of plants common to Florida and the Bahamas and other islands. 
This list excludes weeds, mosses species confined to the coast, and those with fleshy fruits that might be carried by birds. 
2 The Grand Cation of Colorado consists of three components, one § to 13 miles wide, another of 3 to 5, and one less than 1 mile wide, with 
depths of 2000, 1000, and 3000 feet (for the innermost gorge). 
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