DEEP-SEA FOKMATIONS. MJi 



of the oceanic fauna and flora of the present day are found 

 within the hundred-fathom line. In attempting either to define 

 or to contrast the fauna of the shores and of the deep, we find 

 a neutral region, characterized perhaps by no forms strictly its 

 own, but in which the stragglers from each zone flourish, and 

 nothing typical either of the littoral or of the deep-sea fauna 

 is any longer found. 



In many localities where deep-sea deposits are taking place at 

 the present day, the distance from the coast is often not very 

 great, especially in volcanic regions. Along the face of the 

 whole Atlantic coast from the Bahamas to St. Thomas, the line 

 between the continental curve and the two-thousand-fathom line 

 is nowhere more than fifteen miles distant. We cannot there- 

 fore infer that because a formation has been deposited parallel 

 to a continental coast it must necessarily be a shallow-water 

 formation. What to-day would be called continental forma- 

 tions, from the character of their fauna, lie within the limits of 

 say three hundred and fifty to seven hundred and fifty, or per- 

 haps one thousand fathoms. But as the character of the fauna 

 in its turn depends mainly upon the constitution of the bottom, 

 this interdependence introduces many variable elements. There 

 is no greater contrast than that which exists between the fauna 

 living upon the recent limestones of the steep slopes of the 

 Florida plateau and that found at similar depths in the calca- 

 reous ooze of the trough of the Gulf Stream in localities not 

 many miles distant. 



We are justified in considering deposits containing large 

 amounts of globigerina, radiolarian, and diatom mud as pelagic 

 deposits laid down at certain distances from land in considerable 

 depths ; but, as these animals are pelagic, the possibility exists 

 of their being found in shallow deposits. Pelagic foraminifera 

 are found in the muds w hich have been brought down by rivers 

 into the Gulf of Mexico. The modern greensand found oft' 

 the coast of the Carolinas on the edge of the Gulf Stream 

 occurs in depths of less than fifty fathoms. Arenaceous fora- 

 minifera are to-day only found in large quantities in deep 

 water. 



If, as Wallich suggests, flints are now formed only in deep-sea 



