194 



THE VOYAGE OF H.M.S. CHALLENGER. 



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On the 27th August, at 2 p.m., St. Paul's Rocks or islets were seen from the 

 masthead at a distance of 18 miles, and at 3 p.m. from the deck, at a distance of 9 

 or 10 miles. 



The depths in the section along the African coast varied from 2575 fathoms to 1750 

 fathoms. From the point where the course of the ship was turned to the westward a 

 nearly level plateau extends for 500 miles, the depth being from 2300 to 2500 fathoms, 

 after which a gradual elevation takes place to 1500 fathoms 150 miles east of St. Paul's 

 Rocks, and then a depression to 1900 fathoms at a distance of 60 miles from the 

 rocks. 



The deposits at the two depths, 2575 and 2500 fathoms, near the African coast, con- 

 tained respectively 30 and 6 per cent, of carbonate of lime, the small percentage in the 

 latter being due to continental debris, but at all the other Stations there was over 50 

 per cent., and at 1850 fathoms in Mid Atlantic the amount reached 90 per cent. In all 

 the deposits the carbonate of lime consisted chiefly of pelagic Foraminifera, Coccoliths, and 

 Rhabdoliths, with a few fragments of Echinoderms and other organisms. An analysis of 

 the mud from the dredge at Station 102 (2450 fathoms) gave 83 per cent, of carbonate 

 of lime. A careful examination of a large quantity of this deposit showed that nearly 

 the whole of the carbonate of lime present consisted of the dead shells of surface organ- 

 isms, and it was estimated that of the 83 per cent, of carbonate of lime, 75 per cent, 

 was due to pelagic Foraminifera, 6 per cent, to Coccoliths, and 2 per cent, to other 

 calcareous Foraminifera, fragments of Echinids, and Ostracodes. Pulvinulina menardii 

 and its variety tumida were the most abundant forms, but Globigerina saccidifera, 

 Globigerina dubia, Globigerina conglobata, and Sphceroidina dehiscens were also very 

 abundant. It is worthy of notice that the majority of the shells were very large ; 

 and the more delicate surface forms, as Hastigerina and Candeina, appeared to be quite 

 absent. The typical Globigerina bidloides did not appear to be present. The Fora- 

 minifera here were thick-shelled and of large size, and it was precisely in this region that 

 the largest specimens of pelagic Foraminifera were obtained on the surface by means of 

 the tow-net. Many of the shells were broken and appeared to be in a crumbling con- 



1 The velocities at St. Paul's Rocks may be affected by the land to windward. 



