234 BARBOUR: ZOOGEOGRAPHY. 



composed of students qualified for field work, under a competent senior, who would visit the 

 ^Yest Indies for a course of post-graduate study, and would look forward to the acquisition 

 of results of considerable scientific interest and value." 



That the general process of island formation has been extremely slow, and 

 that the evolution from a great land mass of almost continental size and perhaps 

 Eocene age, to the present condition of an extensive archipelago took place 

 evenly and without any great regions disappearing below the sea to reappear 

 later, is shown by the distribution of the land animals. These do not appear 

 now to fall into series corresponding in their distribution to the island arcs, but 

 taken altogether form a single, remarkably homogeneous fauna, many character- 

 istic features of which may be traced from Cuba or Jamaica to Grenada. Natur- 

 ally types derived from Central America predominate in Cuba and in Jamaica 

 (Barbour, Bull. M. C. Z., 1910, 52, p. 276), as naturally types derived by the 

 connection with northern South America predominate in Grenada; while in 

 Porto Rico, for example, the fauna is mixed as one would expect it to be. In 

 times past, great stress has been laid on the significance of the great deep in 

 the Virgin group which separates these islands from St. Croix by 2,000 fms. 

 Nevertheless, the same rocks reappear on both sides of the cleft, and the distri- 

 bution of the fauna shows that this cleft has not always existed. Such a deep of 

 limited area between two land masses lying unaffected by it and yet so near at 

 hand, has, by the fact of its depth alone, but little significance. The phenome- 

 non of islands with closely related faunae being separated by a small area of 

 very deep water is met with frequently in all parts of the world. In the East 

 Indies the Ke Islands are connected on the one hand with Ceram by a series of 

 shallows, reefs, and islands; while, so far as is known, only deep water exists 

 between the Ke and Aru groups and Papua. The fauna in Ke shows many 

 Papuan types as well as types derived from Ceram. Such deeps as these are in 

 no wise to be confounded with extensive clefts like that between Jamaica and 

 Cuba, or between Borneo and Celebes. These are very real zoologic boundaries 

 which have existed since the dawn of land life on the earth. Their importance 

 is pointed out especially by the fact that, although they are narrow, yet no inter- 

 change of fauna whatever has taken place across them by "flotsam and jetsam" 

 methods of dispersal. Yet animals should float across these straits as easily as 

 across great stretches of oceans; and this, some writers persist in believing, con- 

 stantly occurs. Eduard Suess in 1893 contributed a very enlightening article 

 to Natural science (1893, 2, p. 180-187) having the title Are great ocean depths 

 permanent? 



