254 PROCEEDINGS OF THE AMERICAN ACADEMY. 



any question. It is strongly supported by the following facts : (1) All 

 parts of the islands now visible are obviously of volcanic origin. (2) The 

 islauds are separated from the mainland by a very considerable depth of 

 ocean (more than 1500 fathoms). (3) The western coast of South 

 America shows no signs of subsidence, but rather of marked elevation in 

 recent geologic time. 



In accordance with this theory of emergence, the flora of the Galapagos 

 Islands is assumed to have been brought to them by the ordinary agents 

 of plant-distribution, namely, the wind, oceanic currents, and migratory 

 birds. Moreover, it is not difficult to see the probable efficiency of these 

 means of seed-transportation in the present case. The islands lie in the 

 course of pretty constant trade winds, doubtless capable of bearing spores 

 and small seeds to a great distance, as winds have been known to carry 

 fine particles of sand and pumice for hundreds of miles. The great ocean 

 current which sweeps along the west coast of Mexico, and the Humboldt 

 Current, which runs northward along the coast of Chili and Peru, both 

 turn westward just in the equatorial belt where the islands lie. That the 

 current between Central America and the Galapagos has considerable 

 seed-carrying power, seems more than probable from the interesting 

 observations of Mr. Alexander Agassiz (1), 59, 69, who while dredging 

 that part of the Pacific found the bottom " strewn thickly with vegetable 

 matter, which came up in great masses in almost every haul of the 

 trawl." He states also that: "The velocity of the currents in the 

 Panama district is very great, sometimes as much as seventy-five miles a 

 day, so that seeds, fruits, masses of vegetation harboring small reptiles, or 

 even large ones, as well as other terrestrial animals, need not be afloat 

 long before they might safely be landed on the shores of the Galapagos." 

 It may here be noted that Hooker (4), 25 G, has shown that a large pro- 

 portion of the plants of the Galapagos Islands are provided with special 

 means of seed-dispersal, — a fact of interest in this connection. 



But, however probable the pelagic origin of the islands seems from the 

 data above presented, Dr. Baur has pointed out what has appeared to be 

 a fatal defect in this theory. For, although it may be quite possible to 

 explain the presence of plants and some animals upon islands of emer- 

 gence, it is much more difficult if not impossible to explain upon the same 

 theory the extraordinary biological relations between these islands them- 

 selves. An examination of the flora shows that many plants on the 

 different islands are nearly related to each other, without being exactly 

 the same. For instance, each of several islands has a peculiar species 

 of Scalesia, a genus confined to* the archipelago. There are also on 



