290 THREE CRUISES OF THE " BLAKE." 



though there are reasons for supposing it was. The ooze which came 

 up from the same place was of a reddish or brownish tinge, and con- 

 tained an immense number of pteropods, heteropods, and pelagic fora- 

 minifera ; the percentage of lime was not so high as in the white chalk 

 rock, and the residue was much darker in color. 



" Calcareous concretions and nodules of manganese were also dredged 

 in this district." ^ 



In the district around the shores of the Antilles there is a 

 gradual transition from the coarser volcanic bottom deposits of 

 shallow waters to the finer sands and muds, which at a distance 

 from the islands pass into ooze. While dredging in the passages 

 between the islands the trawl often came up well filled with 

 rounded pebbles of volcanic rocks. Their shape may be due 

 either to the action of the strong currents rushing between the 

 islands, or perhaps to the disintegrating action of the warm 

 water. This process may account for the abundance of the 

 coarse volcanic sands found in the West Indian waters. Below 

 six or seven hundred fathoms the bottom in the Caribbean is 

 composed of calcareous ooze, consisting in great part of ptero- 

 pod shells, and in a less degree of foraminiferous remains. 



^ "Off the Barbados, in 221 fathoms, face on which serpulse and polyzoa were 



a very hard calcareous concretion was growing. 



obtained, which showed perfectly how " A similar and somewhat larger con- 

 the rock was formed by crystallization of cretiou from 200 fathoms (Station 291) 

 carbonate of lime around the shells of was also obtained off Barbados, which 

 foraminifera and other centres. A zone was much more overgrown with organ- 

 is seen around the shells, composed of isms, and on its upper surface had a large 

 fibro-radiate calcite ; the crystals of cal- cavity in which a hermit-crab, Polycheles 

 cite, coming from the various centres, Agassizii, had lived. (See Bulletin M. 

 abut against each other, and frequently C. Z;, VIII. Xo. 1.) 

 leave an empty space between them. " Off the north coast of San Domingo, 

 When these spaces are filled by a further in 772 fathoms (Station Xo. VI), were 

 deposition of lime, the whole becomes obtained several small manganese nodules 

 very compact and massive. and a few fragments of a Corallium 



" The centres of the foraminifera are coated \vith manganese, precisely similar 



frequently filled with a gray or yellowish to that dredged by the ' Challenger ' in 



substance, which does not, however, give 1,525 fathoms near Cape Verde. (See 



the reactions of phosphate of lime. Narrative of the Challenger, p. 125.) 



" The mineral particles were very few The nodules were of a light brownish 



in number, among them fragments of color inside, composed in all cases of a 



quartz and plagioclase being observed, mass of pelagic foraminifera. The largest 



This concretion was about two inches in of these nodules had a diameter of about 



diameter, and had a rough areolar sur- two inches." 



