^°i89r''] PROCEEDINGS OP THE NATION.^L MUSEUM. 359 

 ORIGIN OF FAUNA AND FLOKA. 



Dr. Baui's coiiti'iitinii arises from the hypothesis tliut only subsi- 

 dence can exphiin what he terms the harmonic distribution of animal 

 and plant life. He says funher on, " that we need only an elevation of 

 about 10,000 feet to connect the (lalapajios with America.'" The pecul- 

 iarities of the flora which he points out and which are referred to else- 

 where in connection with the arid and humid zcnies (ante, page — , he 

 regarded as explicable only by the theory of subsidence; but it seems 

 to me they are fully as well explained in Agassi/\s paper, and so far as 

 the alpine facies of the flora is considered, it may fairly in this respect 

 be compared to that of the rainless belt of tin; South American main- 

 laiul GOO miles to the eastward, and the modifying influences of cold 

 on one side and drouth on the other may be regarded as producing 

 analogous results in dwarfing and otherwise differentiating vegetable 

 life. The theory of subsidence he assumes will explain all these, as w' ell 

 as similar and other ijhenomena which I have not referred to, ''in an 

 absolutely easy manner." It is very doubtful, however, in the present 

 state of our knowledge, whether this, that, or tlie other theory will sat- 

 isfactorily explain «//, but that theory whicli will iairly explain a good 

 portion, by those factors or agencies that are operating directly under 

 our eyes, would seem to be i)referable and entitled to acceptance over 

 another, however plausible and attractive, that involves conjectural 

 and remoter conditions. It seems to me that anyone who has given 

 much thought and attention to tlic study of the geographical distribu- 

 tion of species, and has pursued it to such an extent as to Justify the 

 term investigation, npon a glance at any good map that presents the 

 breadth and range of the great Peruvian current, its velocity and 

 direction, and the contributing influen{;e of the Mexican as well as the 

 Panamic current, which latter no doubt is an important factor, and 

 these combined including in their sweep and embrace the various 

 islands which form this peculiar group, will readily perceive the geo- 

 graphical origin of the species that now inhabit them and tlie direction 

 from which these islands were stocked or peopled. To the continuous 

 or uninterrupted influence of these rivers in the sea, operating without 

 intermission through indetinite centuries, as well as to the jiersistent 

 agency of trade winds, storm winds, and more transient atrial currents, 

 we may find a solution, or key, to say the least, to the greater part of 

 the phenomena, without resorting to topographic displacement or mod- 

 ifi<'.ation of the sea bed of 10,000 to 12,000 feet elevation to explain the 

 few that are less easy or more difficult of explanation. 



MARINE MOLLUSKS. 



Of the marine shells (257 species) less thnn half a score* are indig- 

 enous; of these some, if not all, may prove npon abetter knowledge 

 of the mollusks of the slunes of Central and Scmth America to belong 



* Not iuclusive of dredged or deep water species. 



