Alfred Russel Wallace : Alfred Wallace : A. R. Wallace :
Russel Wallace : Alfred Russell Wallace (sic)

 
 
Discussion of 'On the Delta of the Amazons'
(S103: 1864)

 
Editor Charles H. Smith's Note: Third party description of discussion at the 17 September 1864 meeting of the British Association for the Advancement of Science, printed on page 470 of the 8 October 1964 issue of Athenæum. To link directly to this page, connect with: http://people.wku.edu/charles.smith/wallace/S103.htm


    'On the Delta of the Amazons,' by Mr. H. W. Bates.--The area which geographically constitutes the Delta of the Amazons forms an irregular triangle, measuring about 180 miles each way. Contrary to what might be expected in the mouth of a great river lying on the Equator, the country in and around it has a pleasant and salubrious climate. The islands and neighbouring mainland are not formed wholly of fluvial deposit: this is the case only with a portion of the area, 120 miles distant from the sea; the remaining portion, or that lying nearest the sea having a rocky base and a sandy soil, the product of the disintegration of the rocks. The author concluded that this alluvial portion of the area was the true delta, and that at no very distant period the seaward portion of the present delta formed a series of islands lying off the mouth of the river. These islands he proved to be of great antiquity by an analysis of their Fauna, which showed (in the groups examined) a large proportion of endemic species. The strong affinity of the Fauna of the south side of the delta with that of Guiana also tended to show that the two regions could not have been formerly separated by a gulf 180 miles wide, impassable by these species. Had this been the case, the southern margins would more naturally have been peopled from Brazil further south, there being no known barrier to hinder the migration of species from this direction. All the facts furnished by the physical geography and the Fauna pointed to the result, that an ancient tract of land or chain of islands bridged over the space between Guiana and what are now the southern borders of the Delta.

    Mr. A. R. Wallace confirmed the conclusions of the author of the paper so far as the island of Mexiana was concerned, which lies in the mouth of the Amazons. He found here, when he visited the place in 1849, beds of sandstone, and believed that very little of the land was due to river-deposit. Mexiana was exposed on two sides to the open sea, yet so vast was the volume of fresh water poured from the mouth of the Amazons that even at high tide, when the stream rose 12 feet, the water was always sweet and drinkable, at least near the land.


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