2 INTRODUCTION. 



The general results are exhibited on the map accompanying the 

 paper in the Geograplmclie Mittheilungen^ and representing the bottom off 

 our coast, from Cape Cod to the island of Cuba. The bottom is repre- 

 sented of different colors, according to its principal constituents, Avhich 

 are chiefly of four different kinds, — silicious sand, clay (the " mud " 

 or " ooze " of the charts), Globigerina mud, and coral sand or mud. 

 The silicious sand and the Globigerina mud have the greatest extent. 



Silicious sand is, with few exceptions, the prevailing material 

 from the shore to the hundred-fathoms line. It extends thus, skirting 

 the shore in a broad band narrowing down to a point as far south 

 as Cape Florida, where it ceases altogether, and is replaced by the 

 coral formation, but reappears again on the west coast of the peninsula 

 near Cape Sable. 



Clay or mud occurs to a considerable extent only to the southward 

 of the Vinejard Islands and eastern part of Long Island, in a region 

 knoAvn to naviijcators as the Block Island Soundino-s, and also in a series 

 of depressions off the entrance to New York, called the Mud- Holes. This 

 mud, of a stiff consistenc}^ and dark gray color (called blue or green by 

 the sailors), may be derived from the tertiary formations of which 

 the bluffs off Gay Head, on the island of Martha's Vineyard, are the 

 remainder. 



Outside of the hundred-fithom line we find the Globigerina mud 

 forming the bottom of the Gulf Stream, whose western edge coincides 

 nearly with that line of depth, and of the greater part of the 

 ocean, of the Gulf of Mexico, and of the deep channels separating 

 the Bahama Banks from each other and from the neighboring lands. 

 The discovery of this important formation is generally attributed to 

 the expedition sent out under the command of Lieutenant Berryman, 

 U. S. N., to sound out the path of the Atlantic Telegraph Cable in 

 1855. In reality, however, the discovery was two years earlier. Lieu- 

 tenants Craven and Mafht, U. S. N., having severally, whilst engaged in 

 Gulf Stream explorations, in the service of the Coast Survey, obtained 

 specimens of this formation. (See Proceed. Americ. Assoc, for Advanc. 

 of Science, Cleveland meeting, 1853.) 



An interesting discovery was made by Professor Bailey in examin- 

 ing these specimens, — the transformation, of Foraminifera into green- 

 sand. The origin of the green-sand grains in geological formations had 

 previously been recognized by Ehrenberg; but here we have evidently 

 the process going on at the present day, particularly along a tract 

 at the meetino; of the silicious and Globio-erina bottoms off the coast 

 of Georgia and South Carolina, and also to a less extent in other places. 

 (The localities are indicated by black dotting on the map quoted ; 

 near the mouth of New York Bay the same sign indicates tertiary 

 green-sand, the continuation of the New Jersey beds.) 



