MUSEUM OF COMPARATIVE ZOOLOGY. 51 



Millolina seminulum Cristellana cultrata 



Spiroculinu impressa C calcar 



Vertebralina striata Sagrina columnella 



ClavuUna communis Uvigerina pygmaa 



C. parisiensis Truncatulina lobatula 



Textularia coiiica Planorbulina sp. 



T. lucidenta Nonionina timbilicatula. 

 T. agglutinans 



Residue, 61.91 per cent, yellowish brown, consists of Minerals [25.00], m. di. 

 0.2 to 0.3 mm. magnetite felspar, quartz, hornblende, and a 'i^sy glassy fragments. 

 Siliceous organisms [25.00], many Sponge spicules, a few Diatoms, one or two 

 Radiolarians, and glauconitic casts of the calcareous organisms. Fine washings 

 [11.91], amorphous clayey matter, with fragments of casts, fine mmerals, and 

 siliceous particles. 



4. Specimens of deposits procured in the Gulf of Mexico and in the 

 Florida Strait. 



During the years 1875, 1876, 1877, and 1878, very extensive series 

 of soundings wei'e obtained at all depths, and in all parts of the above 

 areas. 



There is a very great variety in the shallow water deposits under 100 

 fathoms. Near the coasts of the North American continent, where 

 rivers enter, and where there are few coral reefs, the deposits are either 

 sands or fine clayey muds, formed of detrital matter brought down from 

 the land. Where the shores are lined by coral reefs, the deposits are 

 chiefly made up of coral debris, the shells of pelagic Foramiuifera and 

 Mollusks and other calcareous organisms. 



The character of the deposits in depths greater than 100 fathoms is 

 likewise largely determined by the greater or less proximity to the 

 embouchure of rivers or to coral reefs. 



In all the deeper deposits in the Gulf of Mexico and Strait of Florida, 

 the crystalline mineral particles are very small, rarely exceeding one- 

 tenth of a millimetre in diameter. They consist principally of small 

 rounded grains of quartz, with fragments of felspars, mica, horn- 

 blende, augite, magnetite, and rarely tourmaline. In a few places there 

 were fragments of pumice, and glauconitic particles were occasionally 

 noticed. The mineral particles and fine clayey matter appear to be 

 almost wholly derived from North American rivers. 



The carbonate of lime in the deposits of these regions is mostly made 

 up of the shells of pelagic Foramiuifera and Mollusks. In depths greater 



