HOMOIOZOIC BELTS. 235 



of an elevated temperature in the presence of such tropical or sub- 

 tropical genera as Voluta, Cyprsea, and Oliva, whose remains occur 

 associated with the other genera already referred to, and whose 

 actual range extended at least as far north as at the present dny, 

 and in the case of Voluta still farther. 



The conclusions reached by European geologists as to the exist- 

 ence of two distinct belts or provinces in the Cretaceous area — a 

 Mediterranean and a Baltic — have also been applied by Roemer " to 

 the equivalent deposits occurring on the east and south American 

 borders. The New Jersey greensands (Sennonian), for example, are 

 petrographically and oryctographically correlated with the Upper 

 Cretaceous deposits of Northern Europe, and more particularly with 

 those of Northwest Germany, whereas the Texas basin is placed in 

 a similar relation with the '' Mediterranean " zone of Southern Eu- 

 rope. The much more southerly position of the American beds 

 relatively to the European is taken as conclusive evidence, not only 

 that the present climatic variation on the opposite sides of the At- 

 lantic, for the same parallels of latitude, had already then existed, 

 but also the existence of a well-defined northeasterly trending 

 current of warmer water, or Gulf Stream. That the New Jersey 

 Cretaceous fauna departs most widely from the Texan cannot be 

 denied ; but the evidence is far from conclusive that this variation 

 is the result of direct climatic influences. At the present day the 

 fauna of the Gulf maybe considered as a homogeneous whole, being 

 represented by mucli the same forms along its northern, western, 

 and southern contours. On the other hand, it differs almost wholly 

 from the fauna of the east Atlantic coast, although there can be but 

 little doubt that, were it not for the peninsula of Florida, a consid- 

 erable number of the forms now occurring exclusively on the east 

 coast would have found their way into the Gulf basin as well. 

 During the Cretaceous period the intermixture of east and south 

 coast species was very large, but, contrary to what might have been 

 expected, and directly opposed to Professor Roemer's conclusions, 

 the Gulf fauna, or that corresponding to an enlargement of the 

 present Gulf area, appears to have been in itself of a very clearly 

 recognisable multiple character. From the list of Cretaceous fossils 

 of the United States, prepared by Mr. Meek, in 1864," it would seem 

 that, of some one hundred and sixty species belonging to the State 

 of New Jersey, no less than fifty, or nearly one-third, are also com- 

 16 



