LI>"'NEAN SOCIETY OF LONDON. 39 



out a series of most successful trawlings, exceeding a hundred in 

 number. 



The ' Challenger ' only touched at two of the Virgin Islands, 

 Sombrero and St. Thomas ; and by two successful hauls had a 

 taste of a fauna which, in Prof. Agassiz's opinion, is unequalled 

 in richness of forms and individuals. Indeed, the haul near 

 St. Thomas in 390 fathoms proved to be one of the most extra- 

 ordinary successes of the expedition. It included over 350 speci- 

 mens of invertebrates, belonging to about 245 species, of which 

 129 were new. As a whole the haul was faii'ly representative of 

 the composition of the Caribbean fauna. 



I cannot leave this field of work of the U.S. Coast Survey 

 without referring by a word or two to the thoroughly scieutific 

 manner in wliich the naturalists attached to these cruises 

 have carried out their task from the beginning to the end, thereby 

 raising the character of their work far above one of local interest 

 and importance. Pourtales worked with the spirit of Louis 

 Agassiz, who himself followed these investigations with deep 

 interest, and shortly afterwards, together with Pourtales, joined 

 the ' Hassler ' expedition to the Pacific. Pourtales applied his 

 experience of abyssal conditions and life to an attempt to trace 

 the history of geological formations and of their fossil remains. 

 The Deep Sea opened up to him important questions, such as the 

 affinity of the living Caribbean Corals to those of the European 

 Tertiary. He had defined in the Florida district a zone, inter- 

 mediate between the littoi'al and abyssal, running in the form of 

 a band, 10-12 miles broad, parallel to the reef, with an initial 

 depth of 90 fathoms increasing to 300. Its bottom is recent 

 limestone-rock and peopled with a multitude of animals of all 

 classes. Louis Agassiz, who named this zone the Pourtales- 

 plateau, compared its limestone-formation to the concretionary 

 limestone of the " Coral Rag " ; and he adds that in the whole of 

 the stratified crust of our globe there is no part which has been 

 formed in very deep waters. " If this be so, we shall have to admit 

 that the areas now occupied by our continents, as circumscribed 

 by the 200 fathoms curve or thereabouts, and the oceans, at greater 

 depth, have from the beginning retained their relative outline 

 and po.-ition." Continents have always been areas of gradual 

 upheaval, with weak oscillations, while the oceans have always 

 been areas of sub^^idence. I have already referred to this view 

 of Agassiz, which is shared by J. Murray and others, but cannot 

 be accepted by the student of the terrestrial fauna. 



By a study of the Echinoderms of this area, the attention of 

 Pourtales was directed to the close affinity of the faunae of both 

 sides of the Isthmus of Panama, which he attributes to a former 

 communication between the two oceans. Alex. Agassiz expresses 

 himself still more explicitly on this point (see p. 42). He has 

 no doubt that before the Cretaceous period the Gulf of Mexico 

 and the Caribbean Sea were in freer commuuication. with the 



