ANCIENT CENTRAL AMERICA 
239 
America. The second test is that of the fossil mammals of 
North America. It was pointed out that., as no trace of typi¬ 
cally South American species occur in North American Oligo- 
cene or Miocene deposits, the two continents must have been 
separated by a sea during the period in which these beds were 
laid down. Let us examine these evidences more closely. 
A good many writers have discussed the problem of the 
former junction of the Pacific and Atlantic Oceans across 
Centra] America, from a purely biological point of view. Pro¬ 
fessor Gregory,* who last summarised the subject, came to the 
conclusion that the waterway across Central America was 
finally closed in the Lower Miocene, or possibly even in the 
Upper Oligocene. Among others he alluded to the researches 
of the two Agassiz, father and son, stating that, from a study 
of the sea-urchins, they proposed to date the junction of the 
two oceans much further back. These zoologists referred the 
separation of the two oceans and the formation of the Gulf 
Stream, to the period at the close of the Cretaceous, that is to 
say, to the end of the Secondary Era. Professor Verrill f 
finds that no species of corals are identical on the two sides 
of Central America, while even the genera and families show 
remarkable contrasts. The numerous genera and families of 
reef-building corals, so abundant on the Atlantic side, are 
wholly wanting on the Pacific, with the exception of Porites, 
which is represented by three or* four small species. 
Mr. Belt J maintained that the marine mollusks on the two 
coasts separated by the narrow isthmus of Darien were almost 
entirely distinct. So remarkably distinct are the two faunas, 
he says, that most zoologists consider that there has been no 
communication in the tropics between the Pacific and Atlantic 
Oceans since the close of the Miocene Period. An apparently 
rather remote junction of the two oceans is suggested by 
all these authors, but none of them express any very strong 
convictions on the subject. Dr. Ortmann, on the other hand, 
states that the affinities of the Decapod fauna of the Atlantic 
and Pacific are unmistakable, and that we have ample and con¬ 
vincing evidence of a former connection between these oceans. 
* Gregory, J. W., “Palaeontology of the West Indies,’’ pp. 304—305. 
f Verrill, A. E., “ Comparison of Coral Faunae,” p, 500. 
| Belt, Th., “Naturalist in Nicaragua,” p. 264, 
