262 THE PHYSICAL GEOGRAPHY OF THE SEA. 



bad in quality, yielding representatives of most of the great 

 groups of microscopic organisms usually found in marine sedi- 

 ments. 



" The predominant forms are silicious spicules of sponges. Va- 

 rious forms of these occur ; some long and spindle-shaped or acic- 

 ular, others pin-headed, some three-spined, etc.,. etc. 



*' The Diatoms (silicious infusoria of Ehrenberg) are very few 

 in number, and mostly fragmentary. I found, however, some per- 

 fect valves of a Coscinodiscus. 



" The Foraminifera (Polythalamia of Ehrenburg) are very rare, 

 only one perfect shell being seen, with a few fragments of others. 



" The Polycistini^ are present, and some species of Haliomma 

 were quite perfect. Fragments of other forms of this group indi- 

 cate that various interesting species might be obtained if we had 

 more of the material. 



754. "You see by the above that this deep-sounding differs 

 considerably from those obtained in the Atlantic. The Atlantic 

 soundings were almost wholly composed of calcareous shells of 

 the Foraminifera ; these, on the contrary, contain very few Fora- 

 minifera, and are of a silicious rather than of a calcareous nature. 

 This only makes the condition of things in the northern Atlantic 

 the more interesting, because," says this philosopher, "they prove 

 that deep water is not necessarily underlaid by foraminiferous de- 

 posits, and that some peculiar local conditions of temperature, cur- 

 rents, or geological substratum, have made the North Atlantic a 

 perfect vivarium for the calcareous forms. 



755. "The chart (Plate IX.) you send is very interesting, and 

 combines a wonderful amount of interesting phenomena. I have 

 little doubt that the history of the bottom of the ocean, as record- 

 ed by the sediments, would show a close relation to the facts de- 

 termined for the surface, besides many unexpected relations. I 

 am very anxious to get some soundings from the great ocean cur- 

 rent that, as shown in your chart, sweeps in through the Carib- 

 bean Sea and along the coast of Mexico and Texas. 



756. " I observe on your chart something which looks like a 

 sargasso sea southeast of Madagascar. Is it so ? Get sound- 

 ings, if possible, in these sargasso seas. Get soundings any where 



