122 THREE CRUISES OF THE " BLAKE." 



Pacific, and of their fossil remains, if any are to be found, taken 

 in connectiDn with the bathymetric knowledge we have lately 

 acquired, would go far towards solving these problems. The 

 flora alone can hardly give us the necessary facts. 



Tlie fossil marine fauna, while it can do something to help us 

 to reconstruct the probable route of the oceanic currents, gives 

 us no clue to land connections. Neither does the distribution 

 of the birds, nor that of the reptiles or of the land shells, if we 

 are to judge by the case of the West Indies, Galapagos, and 

 Bermudas. The simplest assumption we can make for these 

 islands is that the drift carried by the existing currents for a 

 long period of time is amply sufficient to account for the pre- 

 sence of their few reptiles, mollusks, and even their mammals, 

 and for the distribution of their flora, without the existence at 

 any time of a direct laud connection.^ 



In the case of New Zealand — an island for a long period of 

 time disconnected from continental masses, except perhaps by 

 its northern extension toward Australia — we account for the 

 South American elements of its fauna by the action of the cur- 

 rents. As yet we know positively of no South American mam- 

 mal element, and the birds have undoubtedly, as has been 

 concluded by Captain Hutton, been derived from the north. 

 The same would hold good of the antarctic elements. This 

 seems a more natural explanation than the attempts made to 

 cite plateaux of not less than two thousand fathoms in depth as 

 proof of a former continental extension, when, for aught we 

 know, these plateaux may be forming and increasing at the 

 present day. No better example of the fallacy of such reason- 

 ing can be given than the phenomena of the growth of the 

 great limestone plateaux of Yucatan and Florida, which we 



1 The changes constantly going on over England formerly extended many miles 



the continental shelf illustrate admira- beyond the present shores, and is still 



bly what is meant by a former land con- slowly washed away by the action of 



nection of continental islands. In a tides, winds, and currents. This sheet of 



letter to Professor Benjamin Peirce, drift once extended in unbroken conti- 



Superintendent of the United States Coast nuity from Cape Ann to Cape Cod, and 



Survey, Professor Agassiz thus referred, farther south ; ... it is constantly di- 



in 1867, to the shoals and islands lying minishing, and, in centuries to come, the 



to the eastward and southward of Cape whole peninsula of Cape Cod may disap- 



Cod : " The drift of the coast of New pear." (See Fig. 60.) 



